(This foreword is not a part of American National Standard for Information Systems — Programming Language C, X3.???-1988.)
American National Standard Programming Language C specifies the syntax and semantics of programs written in the C programming language. It specifies the C program's interactions with the execution environment via input and output data. It also specifies restrictions and limits imposed upon conforming implementations of C language translators.
The standard was developed by the X3J11 Technical Committee on the C Programming Language under project 381-D by American National Standards Committee on Computers and Information Processing (X3). SPARC document number 83-079 describes the purpose of this project to “provide an unambiguous and machine-independent definition of the language C.”
The need for a single clearly defined standard had arisen in the C community due to a rapidly expanding use of the C programming language and the variety of differing translator implementations that had been and were being developed. The existence of similar but incompatible implementations was a serious problem for program developers who wished to develop code that would compile and execute as expected in several different environments.
Part of this problem could be traced to the fact that implementors did not have an adequate definition of the C language upon which to base their implementations. The de facto C programming language standard, The C Programming Language by Brian W. Kernighan and Dennis M. Ritchie, is an excellent book; however, it is not precise or complete enough to specify the C language fully. In addition, the language has grown over years of use to incorporate new ideas in programming and to address some of the weaknesses of the original language.
American National Standard Programming Language C addresses the problems of both the program developer and the translator implementor by specifying the C language precisely.
The work of X3J11 began in the summer of 1983, based on the several documents that were made available to the Committee (see 1.5, Base Documents). The Committee divided the effort into three pieces: the environment, the language, and the library. A complete specification in each of these areas is necessary if truly portable programs are to be developed. Each of these areas is addressed in the Standard. The Committee evaluated many proposals for additions, deletions, and changes to the base documents during its deliberations. A concerted effort was made to codify existing practice wherever unambiguous and consistent practice could be identified. However, where no consistent practice could be identified, the Committee worked to establish clear rules that were consistent with the overall flavor of the language.
This document was approved as an American National Standard by the American National Standards Institute (ANSI) on DD MM, 1988. Suggestions for improvement of this Standard are welcome. They should be sent to the American National Standards Institute, 1430 Broadway, New York, NY 10018.
The Standard was processed and approved for submittal to ANSI by the American National Standards Committee on Computers and Information Processing, X3. Committee approval of the Standard does not necessarily imply that all members voted for its approval. At the time that it approved this Standard, the X3 Committee had the following members:
Organization Name of Representative (To be completed on approval of the Standard.)
Technical Committee X3J11 on the C Programming Language had the following members at the time they forwarded this document to X3 for processing as an American National Standard:
Chair Jim Brodie
Vice-Chair Thomas Plum Plum Hall Secretary P. J. Plauger Whitesmiths, Ltd.
International Representative P. J. Plauger Whitesmiths, Ltd. Steve Hersee Lattice, Inc.
Vocabulary Representative Andrew Johnson Prime Computer
Environment Subcommittee Chairs Ralph Ryan Microsoft Ralph Phraner Phraner Associates
Language Subcommittee Chair Lawrence Rosler AT&T
Library Subcommittee Chair P. J. Plauger Whitesmiths, Ltd.
Draft Redactor David F. Prosser AT&T Lawrence Rosler AT&T
Rationale Redactor Randy Hudson Intermetrics, Inc.
In the following list, unmarked names denote principal members and * denotes alternate members.
David F. Prosser, AT&T Steven J. Adamski, AT&T* (X3H2 SQL liaison) Bob Gottlieb, Alliant Computer Systems Kevin Brosnan, Alliant Computer Systems Neal Weidenhofer, Amdahl Philip C. Steel, American Cimflex Eric McGlohon, American Cimflex* Stephen Kafka, Analog Devices Kevin Leary, Analog Devices* Gordon Sterling, Analog Devices* John Peyton, Apollo Computer Elizabeth Crockett, Apple Computers Ed Wells, Arinc Tom Ketterhagen, Arinc* Vaughn Vernon, Aspen Scientific Craig Bordelon, Bell Communications Research Steve Carter, Bell Communications Research* William Puig, Bell Communications Research* Bob Jervis, Borland International Yom-Tov Meged, Boston Systems Office Rose Thomson, Boston Systems Office* Maurice Fathi, COSMIC John Wu, Charles River Data Systems Daniel Mickey, Chemical Abstracts Service Thomas Mimlitch, Chemical Abstracts Service* Alan Losoff, Chicago Research & Trading Group Edward Briggs, Citibank Firmo Freire, Cobra S/A Jim Patterson, Cognos Bruce Tetelman, Columbia U. Center for Computing Terry Moore, CompuDas Mark Barrenechea, Computer Associates George Eberhardt, Computer Innovations Dave Neathery, Computer Innovations* Joseph Bibbo, Computrition Steve Davies, Concurrent Computer Corporation Don Fosbury, Control Data George VandeBunte, Control Data* Lloyd Irons, Cormorant Communications Tom MacDonald, Cray Research Lynne Johnson, Cray Research* Dave Becker, Cray Research* Jean Risley, Custom Development Environments Rex Jaeschke, DEC Professional Mike Terrazas, DECUS Representative Michael Meissner, Data General Mark Harris, Data General* Leonard Ohmes, Datapoint James Stanley, Data Systems Analysts Samuel J. Kendall, Delft Consulting Randy Meyers, Digital Equipment Corporation Art Bjork, Digital Equipment Corporation* Lu Anne Van de Pas, Digital Equipment Corporation* Ben Patel, EDS Richard Relph, EPI Graham Andrews, Edinburgh Portable Compilers Colin McPhail, Edinburgh Portable Compilers* |
J. Stephen Adamczyk, Edison Design Group Eric Schwarz, Edison Design Group* Dmitry Lenkov, Everest Solutions Frank Farance, Farance Inc. Peter Hayes, Farance Inc.* Florin Jordan, Floradin Philip Provin, General Electric Information Services Liz Sanville, Gould CSD Tina Aleksa, Gould CSD* Thomas Kelly, HCR Corporation Paul Jackson, HCR Corporation* Gary Jeter, Harris Computer Systems Sue Meloy, Hewlett Packard Larry Rosler, Hewlett Packard* Michelle Ruscetta, Hewlett Packard* Thomas E. Osten, Honeywell Information Systems David Kayden, Honeywell Information Systems* Shawn Elliott, IBM Larry Breed, IBM* Mel Goldberg, IBM* Mike Banahan, Instruction Set Clark Nelson, Intel Dan Lau, Intel* John Wolfe, InterACT Lillian Toll, InterACT* Randy Hudson, Intermetrics Keith Winter, International Computers Ltd. Honey M. Schrecker, International Computers Ltd.* Jim Brodie, J. Brodie & Associates Jacklin Kotikian, Kendall Square Research W. Peter Hesse, LSI Logic Europe Ltd. John Kaminski, Language Processors Inc. David Yost, Laurel Arts Mike Branstetter, Lawrence Livermore National Laboratory Bob Weaver, Los Alamos National Laboratory Lidia Eberhart, Modcomp Robert Sherry, Manx Software Courtney Meissen, Mark Williams Co. Patricia Jenkins, Masscomp Dave Hinman, Masscomp* Michael Kearns, MetaLink Tom Pennello, MetaWare Incorporated David F. Weil, Microsoft Mitch Harder, Microsoft* Kim Kempf, Microware Systems Shane McCarron, Minnesota Educational Computing Bruce Olsen, Mosaic Technologies Michael Paton, Motorola Rick Schubert, NCR Brian Johnson, NCR* Joseph Mueller, National Semiconductor Derek Godfrey, National Semiconductor* Jim Upperman, National Bureau of Standards James W. Williams, Naval Research Laboratory Lisa Simon, OCLC Paul Amaranth, Oakland University August R. Hansen, Omniware Michael Rolle, Oracle Carl Ellis, Oregon Software Barry Hedquist, Perennial Sassan Hazeghi, Peritus International James Holmlund, Peritus International* Thomas Plum, Plum Hall Christopher Skelly, Plum Hall* Andrew Johnson, Prime Computer |
Fran Litterio, Prime Computer* Daniel J. Conrad, Prismatics David Fritz, Production Languages Kenneth Pugh, Pugh Killeen Ed Ramsey, Purdue University Stephen Roberts, Purdue University* Kevin Nolan, Quantitative Technology Corp. Robert Mueller, Quantitative Technology Corp.* Chris DeVoney, Que Corporation Jon Tulk, Rabbit Software Terry Colligan, Rational Systems Daniel Saks, Saks & Associates Nancy Saks, Saks & Associates* Oliver Bradley, SAS Institute Alan Beale, SAS Institute* Larry Jones, SDRC Donald Kossman, SEI Information Technology Kenneth Harrenstien, SRI International Larry Rosenthal, Sierra Systems Phil Hempfner, Southern Bell Telephone Purshotam Rajani, Spruce Technology Savu Savulescu, Stagg Systems Peter Darnell, Stellar Computer Lee W. Cooprider, Stellar Computer* Paul Gilmartin, Storage Technology Corp. Steve Muchnick, Sun Microsystems Chuck Rasbold, Supercomputer Systems, Inc. Kelly O'Hair, Supercomputer Systems, Inc.* Henry Richardson, Tandem John M. Hausman, Tandem* Samuel Harbison, Tartan Laboratories Michael S. Ball, TauMetric Carl Sutton, Tektronix Jim Besemer, Tektronix* Reid Tatge, Texas Instruments Ed Brower, Tokheim Robert Mansfield, Tokheim* Monika Khushf, Tymlabs Morgan Jones, Tymlabs* Don Bixler, Unisys Steve Bartels, Unisys* Glenda Berkheimer, Unisys* Annice Jackson, Unisys* Fred Blonder, University of Maryland Fred Schwarz, University of Michigan R. Jordan Kreindler, University of Southern California CTC Mike Carmody, University of Waterloo Douglas Gwyn, US Army BRL (IEEE P1003 liaison) C. Dale Pierce, US Army Management Engineering* John C. Black, VideoFinancial Joseph Musacchia, Wang Labs Fred Rozakis, Wang Labs* P. J. Plauger, Whitesmiths, Ltd. Kim Leeper, Wick Hill Mark Wittenberg, Zehntel Jim Balter Robert Bradbury Edward Chin Neil Daniels Stephen Desofi Michael Duffy Phillip Escue Ralph Phraner D. Hugh Redelmeier Arnold Davi Robbins Roger Wilks Michael J. Young |
This Standard specifies the form and establishes the interpretation of programs written in the C programming language.1
This Standard specifies:
This Standard does not specify:
This document is divided into four major sections:
Examples are provided to illustrate possible forms of the constructions described. Footnotes are provided to emphasize consequences of the rules described in the section or elsewhere in the Standard. References are used to refer to other related sections. A set of appendices summarizes information contained in the Standard. The abstract, the foreword, the examples, the footnotes, the references, and the appendices are not part of the Standard.
The language section (3) is derived from “The C Reference Manual” by Dennis M. Ritchie, a version of which was published as Appendix A of The C Programming Language by Brian W. Kernighan and Dennis M. Ritchie, Prentice-Hall, Inc., 1978; copyright owned by AT&T.
The library section (4) is based on the 1984 /usr/group Standard by the /usr/group Standards Committee, Santa Clara, California, USA (November 14, 1984).
In this Standard, “shall” is to be interpreted as a requirement on an implementation or on a program; conversely, “shall not” is to be interpreted as a prohibition.
The following terms are used in this document:
If a “shall” or “shall not” requirement that appears outside of a constraint is violated, the behavior is undefined. Undefined behavior is otherwise indicated in this Standard by the words “undefined behavior” or by the omission of any explicit definition of behavior. There is no difference in emphasis among these three; they all describe “behavior that is undefined.”
Other terms are defined at their first appearance, indicated by italic type. Terms explicitly defined in this Standard are not to be presumed to refer implicitly to similar terms defined elsewhere.
Terms not defined in this Standard are to be interpreted according to the American National Dictionary for Information Processing Systems, Information Processing Systems Technical Report ANSI X3/TR-1-82 (1982).
Forward references: localization (4.4).
An example of unspecified behavior is the order in which the arguments to a function are evaluated.
An example of undefined behavior is the behavior on integer overflow.
An example of implementation-defined behavior is the propagation of the high-order bit when a signed integer is shifted right.
An example of locale-specific behavior is whether the islower function returns true for characters other than the 26 lower-case English letters.
Forward references: bitwise shift operators (3.3.7), expressions
(3.3), function calls (3.3.2.2), the islower
function (4.3.1.6).
A strictly conforming program shall use only those features of the language and library specified in this Standard. It shall not produce output dependent on any unspecified, undefined, or implementation-defined behavior, and shall not exceed any minimum implementation limit.
The two forms of conforming implementation are hosted and
freestanding. A conforming hosted implementation shall accept any
strictly conforming program. A conforming freestanding implementation
shall accept any strictly conforming program in which the use of the
features specified in the library section (4) is confined to the
contents of the standard headers <float.h>
, <limits.h>
, <stdarg.h>
,
and <stddef.h>
. A conforming implementation may have extensions
(including additional library functions), provided they do not alter
the behavior of any strictly conforming program.
A conforming program is one that is acceptable to a conforming implementation.2
An implementation shall be accompanied by a document that defines all implementation-defined characteristics and all extensions.
Forward references: limits <float.h>
and <limits.h>
(4.1.4), variable
arguments <stdarg.h>
(4.8), common definitions <stddef.h>
(4.1.5).
With the introduction of new devices and extended character sets, new features may be added to the Standard. Subsections in the language and library sections warn implementors and programmers of usages which, though valid in themselves, may conflict with future additions.
Certain features are obsolescent, which means that they may be considered for withdrawal in future revisions of the Standard. They are retained in the Standard because of their widespread use, but their use in new implementations (for implementation features) or new programs (for language or library features) is discouraged.
Forward references: future language directions (3.9), future library directions (4.13).
Symbols in the right margin mark substantive differences between this draft and its predecessor (ANSI X3J11/88-001, January 11, 1988). A plus sign indicates an addition, a minus sign a deletion, and a vertical bar a replacement.
This section and the difference marks themselves will not appear in the published document.
An implementation translates C source files and executes C programs in two data-processing-system environments, which will be called the translation environment and the execution environment in this Standard. Their characteristics define and constrain the results of executing conforming C programs constructed according to the syntactic and semantic rules for conforming implementations.
Forward references: In the environment section (2), only a few of many possible forward references have been noted.
A C program need not all be translated at the same time. The text of the program is kept in units called source files in this Standard. A source file together with all the headers and source files included via the preprocessing directive #include, less any source lines skipped by any of the conditional inclusion preprocessing directives, is called a translation unit. Previously translated translation units may be preserved individually or in libraries. The separate translation units of a program communicate by (for example) calls to functions whose identifiers have external linkage, by manipulation of objects whose identifiers have external linkage, and by manipulation of data files. Translation units may be separately translated and then later linked to produce an executable program.
Forward references: conditional inclusion (3.8.1), linkages of identifiers (3.1.2.2), source file inclusion (3.8.2).
The precedence among the syntax rules of translation is specified by the following phases.3
Forward references: lexical elements (3.1), preprocessing directives (3.8), trigraph sequences (2.2.1.1).
A conforming implementation shall produce at least one diagnostic message (identified in an implementation-defined manner) for every translation unit that contains a violation of any syntax rule or constraint. Diagnostic messages need not be produced in other circumstances.
Two execution environments are defined: freestanding and hosted. In both cases, program startup occurs when a designated C function is called by the execution environment. All objects in static storage shall be initialized (set to their initial values) before program startup. The manner and timing of such initialization are otherwise unspecified. Program termination returns control to the execution environment.
Forward references: initialization (3.5.7).
In a freestanding environment (in which C program execution may take place without any benefit of an operating system), the name and type of the function called at program startup are implementation-defined. There are otherwise no reserved external identifiers. Any library facilities available to a freestanding program are implementation-defined.
The effect of program termination in a freestanding environment is implementation-defined.
A hosted environment need not be provided, but shall conform to the following specifications if present.
The function called at program startup is named main. The implementation declares no prototype for this function. It can be defined with no parameters:
int main(void) { /*...*/ }
or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared):
int main(int argc, char *argv[]) { /*...*/ }
If they are defined, the parameters to the main
function shall obey
the following constraints:
In a hosted environment, a program may use all the functions, macros, type definitions, and objects described in the library section (4).
A return from the initial call to the main
function is equivalent
to calling the exit
function with the value returned by the main
function as its argument. If the main
function executes a return that
specifies no value, the termination status returned to the host
environment is undefined.
Forward references: definition of terms (4.1.1), the exit
function
(4.10.4.3).
The semantic descriptions in this Standard describe the behavior of an abstract machine in which issues of optimization are irrelevant.
Accessing a volatile object, modifying an object, modifying a file, or calling a function that does any of those operations are all side effects,which are changes in the state of the execution environment. Evaluation of an expression may produce side effects. At certain specified points in the execution sequence called sequence points, all side effects of previous evaluations shall be complete and no side effects of subsequent evaluations shall have taken place.
In the abstract machine, all expressions are evaluated as specified by the semantics. An actual implementation need not evaluate part of an expression if it can deduce that its value is not used and that no needed side effects are produced (including any caused by calling a function or accessing a volatile object).
When the processing of the abstract machine is interrupted by receipt of a signal, only the values of objects as of the previous sequence point may be relied on. Objects that may be modified between the previous sequence point and the next sequence point need not have received their correct values yet.
An instance of each object with automatic storage duration is associated with each entry into a block. Such an object exists and retains its last-stored value during the execution of the block and while the block is suspended (by a call of a function or receipt of a signal).
The least requirements on a conforming implementation are:
What constitutes an interactive device is implementation-defined.
More stringent correspondences between abstract and actual semantics may be defined by each implementation.
An implementation might define a one-to-one correspondence between abstract and actual semantics: at every sequence point, the values of the actual objects would agree with those specified by the abstract semantics. The keyword volatile would then be redundant.
Alternatively, an implementation might perform various
optimizations within each translation unit, such that the actual
semantics would agree with the abstract semantics only when making
function calls across translation unit boundaries. In such an
implementation, at the time of each function entry and function return
where the calling
function and the called
function are in different
translation units, the values of all externally linked objects and of
all objects accessible via pointers therein would agree with the
abstract semantics. Furthermore, at the time of each such function
entry the values of the parameters of the called
function and of all
objects accessible via pointers therein would agree with the abstract
semantics. In this type of implementation, objects referred to by
interrupt service routines activated by the signal
function would
require explicit specification of volatile storage, as well as other
implementation-defined restrictions.
In executing the fragment
char c1, c2; /*...*/ c1 = c1 + c2;
the “integral promotions” require that the abstract machine promote the value of each variable to int size and then add the two int s and truncate the sum. Provided the addition of two char s can be done without creating an overflow exception, the actual execution need only produce the same result, possibly omitting the promotions.
Similarly, in the fragment
float f1, f2; double d; /*...*/ f1 = f2 * d;
the multiplication may be executed using single-precision arithmetic if the implementation can ascertain that the result would be the same as if it were executed using double-precision arithmetic (for example, if d were replaced by the constant 2.0, which has type double ). Alternatively, an operation involving only int s or float s may be executed using double-precision operations if neither range nor precision is lost thereby.
Forward references: compound statement, or block (3.6.2), files
(4.9.3), sequence points (3.3, 3.6), the signal
function (4.7),
type qualifiers (3.5.3).
Two sets of characters and their associated collating sequences shall be defined: the set in which source files are written, and the set interpreted in the execution environment. The values of the members of the execution character set are implementation-defined; any additional members beyond those required by this section are locale-specific.
In a character constant or string literal, members of the execution character set shall be represented by corresponding members of the source character set or by escape sequences consisting of the backslash \ followed by one or more characters. A byte with all bits set to 0, called the null character, shall exist in the basic execution character set; it is used to terminate a character string literal.
Both the basic source and basic execution character sets shall have at least the following members: the 26 upper-case letters of the English alphabet
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
the 26 lower-case letters of the English alphabet
a b c d e f g h i j k l m n o p q r s t u v w x y z
the 10 decimal digits
0 1 2 3 4 5 6 7 8 9
the following 29 graphic characters
! " # % & ' ( ) * + , - . / : ; < = > ? [ \ ] ^ _ { | } ~
the space character, and control characters representing horizontal tab, vertical tab, and form feed. In both the source and execution basic character sets, the value of each character after 0 in the above list of decimal digits shall be one greater than the value of the previous. In source files, there shall be some way of indicating the end of each line of text; this Standard treats such an end-of-line indicator as if it were a single new-line character. In the execution character set, there shall be control characters representing alert, backspace, carriage return, and new line. If any other characters are encountered in a source file (except in a preprocessing token that is never converted to a token, a character constant, a string literal, or a comment), the behavior is undefined.
Forward references: character constants (3.1.3.4), preprocessing directives (3.8), string literals (3.1.4), comments (3.1.9).
All occurrences in a source file of the following sequences of three characters (called trigraph sequences5)are replaced with the corresponding single character.
??= # ??( [ ??/ \ ??) ] ??' ^ ??< { ??! | ??> } ??- ~
No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed above is not changed.
The following source line
printf("Eh???/n");
becomes (after replacement of the trigraph sequence ??/ )
printf("Eh?\n");
The source character set may contain multibyte characters, used to represent members of the extended character set. The execution character set may also contain multibyte characters, which need not have the same encoding as for the source character set. For both character sets, the following shall hold:
For the source character set, the following shall hold:
The active position is that location on a display device where the
next character output by the fputc
function would appear. The intent
of writing a printable character (as defined by the isprint
function)
to a display device is to display a graphic representation of that
character at the active position and then advance the active position
to the next position on the current line. The direction of printing
is locale-specific. If the active position is at the final position
of a line (if there is one), the behavior is unspecified.
Alphabetic escape sequences representing nongraphic characters in the execution character set are intended to produce actions on display devices as follows: ( alert ) Produces an audible or visible alert. The active position shall not be changed. ( backspace ) Moves the active position to the previous position on the current line. If the active position is at the initial position of a line, the behavior is unspecified. ( "form feed" ) Moves the active position to the initial position at the start of the next logical page. ( "new line" ) Moves the active position to the initial position of the next line. ( "carriage return" ) Moves the active position to the initial position of the current line. ( "horizontal tab" ) Moves the active position to the next horizontal tabulation position on the current line. If the active position is at or past the last defined horizontal tabulation position, the behavior is unspecified. ( "vertical tab" ) Moves the active position to the initial position of the next vertical tabulation position. If the active position is at or past the last defined vertical tabulation position, the behavior is unspecified.
Each of these escape sequences shall produce a unique implementation-defined value which can be stored in a single char object. The external representations in a text file need not be identical to the internal representations, and are outside the scope of this Standard.
Forward references: the fputc
function (4.9.7.3), the isprint
function (4.3.1.7).
Functions shall be implemented such that they may be interrupted at any time by a signal, or may be called by a signal handler, or both, with no alteration to earlier, but still active, invocations' control flow (after the interruption), function return values, or objects with automatic storage duration. All such objects shall be maintained outside the function image (the instructions that comprise the executable representation of a function) on a per-invocation basis.
The functions in the standard library are not guaranteed to be reentrant and may modify objects with static storage duration.
Both the translation and execution environments constrain the implementation of language translators and libraries. The following summarizes the environmental limits on a conforming implementation.
The implementation shall be able to translate and execute at least one program that contains at least one instance of every one of the following limits:6
A conforming implementation shall document all the limits specified
in this section, which shall be specified in the headers <limits.h>
and <float.h>
.
<limits.h>
The values given below shall be replaced by constant expressions suitable for use in #if preprocessing directives. Their implementation-defined values shall be equal or greater in magnitude (absolute value) to those shown, with the same sign.
CHAR_BIT 8
SCHAR_MIN -127
SCHAR_MAX +127
UCHAR_MAX 255
CHAR_MIN see below
CHAR_MAX see below
MB_LEN_MAX 1
SHRT_MIN -32767
SHRT_MAX +32767
USHRT_MAX 65535
INT_MIN -32767
INT_MAX +32767
UINT_MAX 65535
LONG_MIN -2147483647
LONG_MAX +2147483647
ULONG_MAX 4294967295
If the value of an object of type char sign-extends when used in an expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the value of CHAR_MAX shall be the same as that of SCHAR_MAX. If the value of an object of type char does not sign-extend when used in an expression, the value of CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of UCHAR_MAX.7
<float.h>
delim $$ The characteristics of floating types are defined in terms of a model that describes a representation of floating-point numbers and values that provide information about an implementation's floating-point arithmetic. The following parameters are used to define the model for each floating-point type:
s sign (±1) b base or radix of exponent representation (an intger > 1) e exponent (an integer between a minimum emin and a maximum emax p precision (the nuber of base-b digits in the significand) fk nonnegatove integers less that b (the significand digits)
A normalized floating-point number x (f1 > 0 if x ≠ 0) is defined by the following model:8
x = s × be × ∑pk=1 fk × b-k, emin ≤ e ≤ emax
Of the values in the <float.h>
header, FLT_RADIX shall be a
constant expression suitable for use in #if preprocessing directives;
all other values need not be constant expressions. All except
FLT_RADIX and FLT_ROUNDS have separate names for all three
floating-point types. The floating-point model representation is
provided for all values except FLT_ROUNDS.
The rounding mode for floating-point addition is characterized by the value of FLT_ROUNDS: -1 indeterminable, 0 toward zero, 1 to nearest, 2 toward positive infinity, 3 toward negative infinity. All other values for FLT_ROUNDS characterize implementation-defined rounding behavior.
The values given in the following list shall be replaced by implementation-defined expressions that shall be equal or greater in magnitude (absolute value) to those shown, with the same sign.
FLT_RADIX 2
FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG
⌊(p - 1) × log10b⌋ + 1 if b is a power of 10, 0 otherwise
FLT_DIG 6 DBL_DIG 10 LDBL_DIG 10
FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP
FLT_MIN_10_EXP -37 DBL_MIN_10_EXP -37 LDBL_MIN_10_EXP -37
FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP
FLT_MAX_10_EXP +37 DBL_MAX_10_EXP +37 LDBL_MAX_10_EXP +37
The values given in the following list shall be replaced by implementation-defined expressions with values that shall be equal to or greater than those shown.
FLT_MAX 1E+37 DBL_MAX 1E+37 LDBL_MAX 1E+37
The values given in the following list shall be replaced by implementation-defined expressions with values that shall be equal to or smaller than those shown.
FLT_EPSILON 1E-5 DBL_EPSILON 1E-9 LDBL_EPSILON 1E-9
FLT_MIN 1E-37 DBL_MIN 1E-37 LDBL_MIN 1E-37
The following describes an artificial floating-point representation
that meets the minimum requirements of the Standard, and the
appropriate values in a <float.h>
header for type float:
x = s × 16e × ∑6k=1 fk × 16-k, -31 ≤ e ≤ +32
FLT_RADIX 16 FLT_MANT_DIG 6 FLT_EPSILON 9.53674316E-07F FLT_DIG 6 FLT_MIN_EXP -31 FLT_MIN 2.93873588E-39F FLT_MIN_10_EXP -38 FLT_MAX_EXP +32 FLT_MAX 3.40282347E+38F FLT_MAX_10_EXP +38
The following describes floating-point representations that also
meet the requirements for single-precision and double-precision
normalized numbers in the IEEE Standard for Binary Floating-Point
Arithmetic (ANSI/IEEE Std 754-1985),9 b and the appropriate values
in a <float.h>
header for types float and double:
xf = s × 2e × ∑24k=1 fk × 2-k, -125 ≤ e ≤ +128
xd = s × 2e × ∑53k=1 fk × 2-k, -1021 ≤ e ≤ +1024
FLT_RADIX 2 FLT_MANT_DIG 24 FLT_EPSILON 1.19209290E-07F FLT_DIG 6 FLT_MIN_EXP -125 FLT_MIN 1.17549435E-38F FLT_MIN_10_EXP -37 FLT_MAX_EXP +128 FLT_MAX 3.40282347E+38F FLT_MAX_10_EXP +38 DBL_MANT_DIG 53 DBL_EPSILON 2.2204460492503131E-16 DBL_DIG 15 DBL_MIN_EXP -1021 DBL_MIN 2.2250738585072016E-308 DBL_MIN_10_EXP -307 DBL_MAX_EXP +1024 DBL_MAX 1.7976931348623157E+308 DBL_MAX_10_EXP +308
The values shown above for FLT_EPSILON and DBL_EPSILON are appropriate for the ANSI/IEEE Std 754-1985 default rounding mode (to nearest). Their values may differ for other rounding modes.
Forward references: conditional inclusion (3.8.1). conditional inclusion (3.8.1).
In the syntax notation used in the language section (3), syntactic categories (nonterminals) are indicated by italic type, and literal words and character set members (terminals) by bold type. A colon (:) following a nonterminal introduces its definition. Alternative definitions are listed on separate lines, except when prefaced by the words “one of.” An optional symbol is indicated by the subscript “opt,” so that
{ expressionopt }
indicates an optional expression enclosed in braces.
token: keyword identifier constant string-literal operator punctuator
preprocessing-token: header-name identifier pp-number character-constant string-literal operator punctuator each non-white-space character that cannot be one of the above
Each preprocessing token that is converted to a token shall have the lexical form of a keyword, an identifier, a constant, a string literal, an operator, or a punctuator.
A token is the minimal lexical element of the language in translation phases 7 and 8. The categories of tokens are: keywords, identifiers, constants, string literals, operators, and punctuators. A preprocessing token is the minimal lexical element of the language in translation phases 3 through 6. The categories of preprocessing token are: header names, identifiers, preprocessing numbers, character constants, string literals, operators, punctuators, and single non-white-space characters that do not lexically match the other preprocessing token categories. If a ' or a " character matches the last category, the behavior is undefined. Comments (described later) and the characters space, horizontal tab, new-line, vertical tab, and form-feed—collectively called white space—can separate preprocessing tokens. As described in 3.8, in certain circumstances during translation phase 4, white space (or the absence thereof) serves as more than preprocessing token separation. White space may appear within a preprocessing token only as part of a header name or between the quotation characters in a character constant or string literal.
If the input stream has been parsed into preprocessing tokens up to a given character, the next preprocessing token is the longest sequence of characters that could constitute a preprocessing token.
The program fragment 1Ex is parsed as a preprocessing number token (one that is not a valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex might produce a valid expression (for example, if Ex were a macro defined as +1 ). Similarly, the program fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or not E is a macro name.
The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on increment operators, even though the parse x ++ + ++ y might yield a correct expression.
Forward references: character constants (3.1.3.4), comments (3.1.9), expressions (3.3), floating constants (3.1.3.1), header names (3.1.7), macro replacement (3.8.3), postfix increment and decrement operators (3.3.2.4), prefix increment and decrement operators (3.3.3.1), preprocessing directives (3.8), preprocessing numbers (3.1.8), string literals (3.1.4).
keyword: one of auto double int struct break else long switch case enum register typedef char extern return union const float short unsigned continue for signed void default goto sizeof volatile do if static while
The above tokens (entirely in lower-case) are reserved (in translation phases 7 and 8) for use as keywords, and shall not be used otherwise.
identifier: nondigit identifier nondigit identifier digit
nondigit: one of _ a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
digit: one of 0 1 2 3 4 5 6 7 8 9
An identifier is a sequence of nondigit characters (including the underscore _ and the lower-case and upper-case letters) and digits. The first character shall be a nondigit character.
In translation phases 7 and 8, an identifier shall not consist of the same sequence of characters as a keyword.
An identifier denotes an object, a function, or one of the following entities that will be described later: a tag or a member of a structure, union, or enumeration; a typedef name; a label name; a macro name; or a macro parameter. A member of an enumeration is called an enumeration constant. Macro names and macro parameters are not considered further here, because prior to the semantic phase of program translation any occurrences of macro names in the source file are replaced by the preprocessing token sequences that constitute their macro definitions.
There is no specific limit on the maximum length of an identifier.
The implementation shall treat at least the first 31 characters of an internal name (a macro name or an identifier that does not have external linkage) as significant. Corresponding lower-case and upper-case letters are different. The implementation may further restrict the significance of an external name (an identifier that has external linkage) to six characters and may ignore distinctions of alphabetical case for such names.10 These limitations on identifiers are all implementation-defined.
Any identifiers that differ in a significant character are different identifiers. If two identifiers differ in a non-significant character, the behavior is undefined.
Forward references: linkages of identifiers (3.1.2.2), macro replacement (3.8.3).
An identifier is visible (i.e., can be used) only within a region of program text called its scope. There are four kinds of scopes: function, file, block, and function prototype. (A function prototype is a declaration of a function that declares the types of its parameters.)
A label name is the only kind of identifier that has function scope. It can be used (in a goto statement) anywhere in the function in which it appears, and is declared implicitly by its syntactic appearance (followed by a : and a statement). Label names shall be unique within a function.
Every other identifier has scope determined by the placement of its declaration (in a declarator or type specifier). If the declarator or type specifier that declares the identifier appears outside of any block or list of parameters, the identifier has file scope, which terminates at the end of the translation unit. If the declarator or type specifier that declares the identifier appears inside a block or within the list of parameter declarations in a function definition, the identifier has block scope, which terminates at the } that closes the associated block. If the declarator or type specifier that declares the identifier appears within the list of parameter declarations in a function prototype (not part of a function definition), the identifier has function prototype scope,which terminates at the end of the function declarator. If an outer declaration of a lexically identical identifier exists in the same name space, it is hidden until the current scope terminates, after which it again becomes visible.
Structure, union, and enumeration tags have scope that begins just after the appearance of the tag in a type specifier that declares the tag. Each enumeration constant has scope that begins just after the appearance of its defining enumerator in an enumerator list. Any other identifier has scope that begins just after the completion of its declarator.
Forward references: compound statement, or block (3.6.2), declarations (3.5), enumeration specifiers (3.5.2.2), function calls (3.3.2.2), function declarators (including prototypes) (3.5.4.3), function definitions (3.7.1), the goto statement (3.6.6.1), labeled statements (3.6.1), name spaces of identifiers (3.1.2.3), scope of macro definitions (3.8.3.5), source file inclusion (3.8.2), tags (3.5.2.3), type specifiers (3.5.2).
An identifier declared in different scopes or in the same scope more than once can be made to refer to the same object or function by a process called linkage. There are three kinds of linkage: external, internal, and none.
In the set of translation units and libraries that constitutes an entire program, each instance of a particular identifier with external linkage denotes the same object or function. Within one translation unit, each instance of an identifier with internal linkage denotes the same object or function. Identifiers with no linkage denote unique entities.
If the declaration of an identifier for an object or a function has file scope and contains the storage-class specifier static, the identifier has internal linkage.
If the declaration of an identifier for an object or a function contains the storage-class specifier extern, the identifier has the same linkage as any visible declaration of the identifier with file scope. If there is no visible declaration with file scope, the identifier has external linkage.
If the declaration of an identifier for a function has no storage-class specifier, its linkage is determined exactly as if it were declared with the storage-class specifier extern. If the declaration of an identifier for an object has file scope and no storage-class specifier, its linkage is external.
The following identifiers have no linkage: an identifier declared to be anything other than an object or a function; an identifier declared to be a function parameter; an identifier declared to be an object inside a block without the storage-class specifier extern.
If, within a translation unit, the same identifier appears with both internal and external linkage, the behavior is undefined.
Forward references: compound statement, or block (3.6.2), declarations (3.5), expressions (3.3), external definitions (3.7).
If more than one declaration of a particular identifier is visible at any point in a translation unit, the syntactic context disambiguates uses that refer to different entities. Thus, there are separate name spaces for various categories of identifiers, as follows:
Forward references: declarators (3.5.4), enumeration specifiers (3.5.2.2), labeled statements (3.6.1), structure and union specifiers (3.5.2.1), structure and union members (3.3.2.3), tags (3.5.2.3).
An object has a storage duration that determines its lifetime. There are two storage durations: static and automatic.
An object declared with external or internal linkage, or with the storage-class specifier static has static storage duration. For such an object, storage is reserved and its stored value is initialized only once, prior to program startup. The object exists and retains its last-stored value throughout the execution of the entire program.12
An object declared with no linkage and without the storage-class specifier static has automatic storage duration. Storage is guaranteed to be reserved for a new instance of such an object on each normal entry into the block in which it is declared, or on a jump from outside the block to a label in the block or in an enclosed block. If an initialization is specified for the value stored in the object, it is performed on each normal entry, but not if the block is entered by a jump to a label. Storage for the object is no longer guaranteed to be reserved when execution of the block ends in any way. (Entering an enclosed block suspends but does not end execution of the enclosing block. Calling a function that returns suspends but does not end execution of the block containing the call.) The value of a pointer that referred to an object with automatic storage duration that is no longer guaranteed to be reserved is indeterminate.
Forward references: compound statement, or block (3.6.2), function calls (3.3.2.2), initialization (3.5.7).
The meaning of a value stored in an object or returned by a function is determined by the type of the expression used to access it. (An identifier declared to be an object is the simplest such expression; the type is specified in the declaration of the identifier.) Types are partitioned into object types (types that describe objects), function types (types that describe functions), and incomplete types (types that describe objects but lack information needed to determine their sizes).
An object declared as type char is large enough to store any member of the basic execution character set. If a member of the required source character set enumerated in 2.2.1 is stored in a char object, its value is guaranteed to be positive. If other quantities are stored in a char object, the behavior is implementation-defined: the values are treated as either signed or nonnegative integers.
There are four signed integer types, designated as signed char, short int, int, and long int. (The signed integer and other types may be designated in several additional ways, as described in 3.5.2.)
An object declared as type signed char occupies the same amount of
storage as a “plain” char object. A “plain” int object has the
natural size suggested by the architecture of the execution
environment (large enough to contain any value in the range INT_MIN to
INT_MAX as defined in the header <limits.h>
). In the list of signed
integer types above, the range of values of each type is a subrange of
the values of the next type in the list.
For each of the signed integer types, there is a corresponding (but different) unsigned integer type (designated with the keyword unsigned) that uses the same amount of storage (including sign information) and has the same alignment requirements. The range of nonnegative values of a signed integer type is a subrange of the corresponding unsigned integer type, and the representation of the same value in each type is the same. A computation involving unsigned operands can never overflow, because a result that cannot be represented by the resulting unsigned integer type is reduced modulo the number that is one greater than the largest value that can be represented by the resulting unsigned integer type.
There are three floating types, designated as float, double, and long double. The set of values of the type float is a subset of the set of values of the type double ; the set of values of the type double is a subset of the set of values of the type long double.
The type char, the signed and unsigned integer types, and the floating types are collectively called the basic types. Even if the implementation defines two or more basic types to have the same representation, they are nevertheless different types.
There are three character types, designated as char, signed char, and unsigned char.
An enumeration comprises a set of named integer constant values. Each distinct enumeration constitutes a different enumerated type.
The void type comprises an empty set of values; it is an incomplete type that cannot be completed.
Any number of derived types can be constructed from the basic, enumerated, and incomplete types, as follows:
These methods of constructing derived types can be applied recursively.
The type char, the signed and unsigned integer types, and the enumerated types are collectively called integral types. The representations of integral types shall define values by use of a pure binary numeration system.13 American National Dictionary for Information Processing Systems.) The representations of floating types are unspecified.
Integral and floating types are collectively called arithmetic types. Arithmetic types and pointer types are collectively called scalar types. Array and structure types are collectively called aggregate types.14
A pointer to void shall have the same representation and alignment requirements as a pointer to a character type. Other pointer types need not have the same representation or alignment requirements.
An array type of unknown size is an incomplete type. It is completed, for an identifier of that type, by specifying the size in a later declaration (with internal or external linkage). A structure or union type of unknown content (as described in 3.5.2.3) is an incomplete type. It is completed, for all declarations of that type, by declaring the same structure or union tag with its defining content later in the same scope.
Array, function, and pointer types are collectively called derived declarator types. A declarator type derivation from a type T is the construction of a derived declarator type from T by the application of an array, a function, or a pointer type derivation to T.
A type is characterized by its top type, which is either the first type named in describing a derived type (as noted above in the construction of derived types), or the type itself if the type consists of no derived types.
A type has qualified type if its top type is specified with a type qualifier; otherwise it has unqualified type. The type qualifiers const and volatile respectively designate const-qualified type and volatile-qualified type.15 For each qualified type there is an unqualified type that is specified the same way as the qualified type, but without any type qualifiers in its top type. This type is known as the unqualified version of the qualified type. Similarly, there are appropriately qualified versions of types (such as a const-qualified version of a type), just as there are appropriately non-qualified versions of types (such as a non-const-qualified version of a type).
The type designated as “float *” is called “pointer to float” and its top type is a pointer type, not a floating type. The const-qualified version of this type is designated as “float * const” whereas the type designated as “ const float * ” is not a qualified type — it is called “pointer to const float ” and is a pointer to a qualified type.
Finally, the type designated as “ struct tag (*[5])(float) ” is called “array of pointer to function returning struct tag.” Its top type is array type. The array has length five and the function has a single parameter of type float.
Forward references: character constants (3.1.3.4), declarations (3.5), tags (3.5.2.3), type qualifiers (3.5.3).
Two types have compatible type if their types are the same. Additional rules for determining whether two types are compatible are described in 3.5.2 for type specifiers, in 3.5.3 for type qualifiers, and in 3.5.4 for declarators.16 Moreover, two structure, union, or enumeration types declared in separate translation units are compatible if they have the same number of members, the same member names, and compatible member types; for two structures, the members shall be in the same order; for two enumerations, the members shall have the same values.
All declarations that refer to the same object or function shall have compatible type; otherwise the behavior is undefined.
A composite type can be constructed from two types that are compatible; it is a type that is compatible with both of the two types and has the following additions:
These rules apply recursively to the types from which the two types are derived.
For an identifier with external or internal linkage declared in the same scope as another declaration for that identifier, the type of the identifier becomes the composite type.
Given the following two file scope declarations:
int f(int (*)(), double (*)[3]); int f(int (*)(char *), double (*)[]);
The resulting composite type for the function is:
int f(int (*)(char *), double (*)[3]);
Forward references: declarators (3.5.4), enumeration specifiers (3.5.2.2), structure and union specifiers (3.5.2.1), type definitions (3.5.6), type qualifiers (3.5.3), type specifiers (3.5.2).
constant: floating-constant integer-constant enumeration-constant character-constant
The value of a constant shall be in the range of representable values for its type.
Each constant has a type, determined by its form and value, as detailed later.
floating-constant: fractional-constant exponent-partopt floating-suffixopt digit-sequence exponent-part floating-suffixopt
fractional-constant: digit-sequenceopt . digit-sequence digit-sequence .
exponent-part: e signopt digit-sequence E signopt digit-sequence
sign: one of + -
digit-sequence: digit digit-sequence digit
floating-suffix: one of f l F L
A floating constant has a value part that may be followed by an exponent part and a suffix that specifies its type. The components of the value part may include a digit sequence representing the whole-number part, followed by a period (.), followed by a digit sequence representing the fraction part. The components of the exponent part are an e or E followed by an exponent consisting of an optionally signed digit sequence. Either the whole-number part or the fraction part shall be present; either the period or the exponent part shall be present.
The value part is interpreted as a decimal rational number; the digit sequence in the exponent part is interpreted as a decimal integer. The exponent indicates the power of 10 by which the value part is to be scaled. If the scaled value is in the range of representable values (for its type) but cannot be represented exactly, the result is either the nearest higher or nearest lower value, chosen in an implementation-defined manner.
An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has type float. If suffixed by the letter l or L, it has type long double.
integer-constant: decimal-constant integer-suffixopt octal-constant integer-suffixopt hexadecimal-constant integer-suffixopt
decimal-constant: nonzero-digit decimal-constant digit
octal-constant: 0 octal-constant octal-digit
hexadecimal-constant: 0x hexadecimal-digit 0X hexadecimal-digit hexadecimal-constant hexadecimal-digit
nonzero-digit: one of 1 2 3 4 5 6 7 8 9
octal-digit: one of 0 1 2 3 4 5 6 7
hexadecimal-digit: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
integer-suffix: unsigned-suffix long-suffixopt long-suffix unsigned-suffixopt
unsigned-suffix: one of u U
long-suffix: one of l L
An integer constant begins with a digit, but has no period or exponent part. It may have a prefix that specifies its base and a suffix that specifies its type.
A decimal constant begins with a nonzero digit and consists of a sequence of decimal digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed by a sequence of the decimal digits and the letters a (or A ) through f (or F) with values 10 through 15 respectively.
The value of a decimal constant is computed base 10; that of an octal constant, base 8; that of a hexadecimal constant, base 16. The lexically first digit is the most significant.
The type of an integer constant is the first of the corresponding list in which its value can be represented. Unsuffixed decimal: int, long int, unsigned long int; unsuffixed octal or hexadecimal: int, unsigned int, long int, unsigned long int; suffixed by the letter u or U: unsigned int, unsigned long int; suffixed by the letter l or L: long int, unsigned long int; suffixed by both the letters u or U and l or L: unsigned long int.
enumeration-constant: identifier
An identifier declared as an enumeration constant has type int.
Forward references: enumeration specifiers (3.5.2.2).
character-constant: ' c-char-sequence ' L' c-char-sequence '
c-char-sequence: c-char c-char-sequence c-char
c-char: any member of the source character set except the single-quote ', backslash \, or new-line character escape-sequence
escape-sequence: simple-escape-sequence octal-escape-sequence hexadecimal-escape-sequence
simple-escape-sequence: one of \' \" \? \\ \a \b \f \n \r \t \v
octal-escape-sequence: \ octal-digit \ octal-digit octal-digit \ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence: \x hexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit
An integer character constant is a sequence of one or more multibyte characters enclosed in single-quotes, as in 'x' or 'ab'. A wide character constant is the same, except prefixed by the letter L. With a few exceptions detailed later, the elements of the sequence are any members of the source character set; they are mapped in an implementation-defined manner to members of the execution character set.
The single-quote ', the double-quote, the question-mark ?, the backslash \, and arbitrary integral values, are representable according to the following table of escape sequences:
single-quote ' \' double-quote " \" question-mark ? \? backslash \ \\ octal integer \ octal digits hexadecimal integer \x hexadecimal digits
The double-quote and question-mark ? are representable either by themselves or by the escape sequences \" and \? respectively, but the single-quote ' and the backslash \ shall be represented, respectively, by the escape sequences \' and \\.
The octal digits that follow the backslash in an octal escape sequence are taken to be part of the construction of a single character for an integer character constant or of a single wide character for a wide character constant. The numerical value of the octal integer so formed specifies the value of the desired character.
The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape sequence are taken to be part of the construction of a single character for an integer character constant or of a single wide character for a wide character constant. The numerical value of the hexadecimal integer so formed specifies the value of the desired character.
Each octal or hexadecimal escape sequence is the longest sequence of characters that can constitute the escape sequence.
In addition, certain nongraphic characters are representable by escape sequences consisting of the backslash \ followed by a lower-case letter: \a, \b, \f, \n, \r, \t, and \v.17 If any other escape sequence is encountered, the behavior is undefined.18
The value of an octal or hexadecimal escape sequence shall be in the range of representable values for the unsigned type corresponding to its type.
An integer character constant has type int. The value of an integer character constant containing a single character that maps into a member of the basic execution character set is the numerical value of the representation of the mapped character interpreted as an integer. The value of an integer character constant containing more than one character, or containing a character or escape sequence not represented in the basic execution character set, is implementation-defined. In particular, in an implementation in which type char has the same range of values as signed char, the high-order bit position of a single-character integer character constant is treated as a sign bit.
A wide character constant has type wchar_t, an integral type
defined in the <stddef.h>
header. The value of a wide character
constant containing a single multibyte character that maps into a
member of the extended execution character set is the wide character
(code) corresponding to that multibyte character, as defined by the
mbtowc function, with an implementation-defined current locale. The
value of a wide character constant containing more than one multibyte
character, or containing a multibyte character or escape sequence not
represented in the extended execution character set, is
implementation-defined.
The construction '\0' is commonly used to represent the null character.
Consider implementations that use two's-complement representation for integers and eight bits for objects that have type char. In an implementation in which type char has the same range of values as signed char, the integer character constant '\xFF' has the value if type char has the same range of values as unsigned char, the character constant '\xFF' has the value
Even if eight bits are used for objects that have type char, the construction '\x123' specifies an integer character constant containing only one character. (The value of this single-character integer character constant is implementation-defined and violates the above constraint.) To specify an integer character constant containing the two characters whose values are 0x12 and '3', the construction '\0223' may be used, since a hexadecimal escape sequence is terminated only by a non-hexadecimal character. (The value of this two-character integer character constant is implementation-defined also.)
Even if 12 or more bits are used for objects that have type wchar_t, the construction L'\1234' specifies the implementation-defined value that results from the combination of the values 0123 and '4'.
Forward references: characters and integers (3.2.1.1) common
definitions <stddef.h>
(4.1.5), the mbtowc
function (4.10.7.2).
string-literal: " s-char-sequenceopt " L" s-char-sequenceopt "
s-char-sequence: s-char s-char-sequence s-char
s-char: any member of the source character set except the double-quote ", backslash \, or new-line character escape-sequence
A character string literal is a sequence of zero or more multibyte characters enclosed in double-quotes, as in xyz. A wide string literal is the same, except prefixed by the letter L.
The same considerations apply to each element of the sequence in a character string literal or a wide string literal as if it were in an integer character constant or a wide character constant, except that the single-quote ' is representable either by itself or by the escape sequence \', but the double-quote shall be represented by the escape sequence \.
A character string literal has static storage duration and type “array of char,” and is initialized with the given characters. A wide string literal has static storage duration and type “array of wchar_t,” and is initialized with the wide characters corresponding to the given multibyte characters. Character string literals that are adjacent tokens are concatenated into a single character string literal. A null character is then appended.19 Likewise, adjacent wide string literal tokens are concatenated into a single wide string literal to which a code with value zero is then appended. If a character string literal token is adjacent to a wide string literal token, the behavior is undefined.
Identical string literals of either form need not be distinct. If the program attempts to modify a string literal of either form, the behavior is undefined.
This pair of adjacent character string literals
"\x12" "3"
produces a single character string literal containing the two characters whose values are \x12 and '3', because escape sequences are converted into single members of the execution character set just prior to adjacent string literal concatenation.
Forward references: common definitions <stddef.h>
(4.1.5).
operator: one of [ ] ( ) . -> ++ -- & * + - ~ ! sizeof / % << >> < > <= >= == != ^ | && || ? : = *= /= %= += -= <<= >>= &= ^= |= , # ##
The operators [ ], ( ), and ? : shall occur in pairs, possibly separated by expressions. The operators # and ## shall occur in macro-defining preprocessing directives only.
An operator specifies an operation to be performed (an evaluation ) that yields a value, or yields a designator, or produces a side effect, or a combination thereof. An operand is an entity on which an operator acts.
Forward references: expressions (3.3), macro replacement (3.8.3).
punctuator: one of [ ] ( ) { } * , : = ; ... #
The punctuators [ ], ( ), and { } shall occur in pairs, possibly separated by expressions, declarations, or statements. The punctuator # shall occur in preprocessing directives only.
A punctuator is a symbol that has independent syntactic and semantic significance but does not specify an operation to be performed that yields a value. Depending on context, the same symbol may also represent an operator or part of an operator.
Forward references: expressions (3.3), declarations (3.5), preprocessing directives (3.8), statements (3.6).
header-name: < h-char-sequence > " q-char-sequence "
h-char-sequence: h-char h-char-sequence h-char
h-char: any member of the source character set except the new-line character and >
q-char-sequence: q-char q-char-sequence q-char
q-char: any member of the source character set except the new-line character and "
Header name preprocessing tokens shall only appear within a #include preprocessing directive.
The sequences in both forms of header names are mapped in an implementation-defined manner to headers or external source file names as specified in 3.8.2.
If the characters ', \, ", or /* occur in the sequence between the < and > delimiters, the behavior is undefined. Similarly, if the characters ', \, or /* occur in the sequence between the " delimiters, the behavior is undefined.20
The following sequence of characters:
0x3<1/a.h>1e2 #include <1/a.h> #define const.member@$
forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited by a { on the left and a } on the right).
{0x3}{<}{1}{/}{a}{.}{h}{>}{1e2} {#}{include} {<1/a.h>} {#}{define} {const}{.}{member}{@}{$}
Forward references: source file inclusion (3.8.2).
pp-number: digit . digit pp-number digit pp-number nondigit pp-number e sign pp-number E sign pp-number .
A preprocessing number begins with a digit optionally preceded by a period (.) and may be followed by letters, underscores, digits, periods, and e+, e-, E+, or E- character sequences.
Preprocessing number tokens lexically include all floating and integer constant tokens.
A preprocessing number does not have type or a value; it acquires both after a successful conversion (as part of translation phase 7) to a floating constant token or an integer constant token.
Except within a character constant, a string literal, or a comment, the characters /* introduce a comment. The contents of a comment are examined only to identify multibyte characters and to find the characters */ that terminate it.21
Several operators convert operand values from one type to another automatically. This section specifies the result required from such an implicit conversion, as well as those that result from a cast operation (an explicit conversion). The list in 3.2.1.5 summarizes the conversions performed by most ordinary operators; it is supplemented as required by the discussion of each operator in 3.3.
Conversion of an operand value to a compatible type causes no change.
Forward references: cast operators (3.3.4).
A char, a short int, or an int bit-field, or their signed or unsigned varieties, or an object that has enumeration type, may be used in an expression wherever an int or unsigned int may be used. If an int can represent all values of the original type, the value is converted to an int; otherwise it is converted to an unsigned int. These are called the integral promotions.
The integral promotions preserve value including sign. As discussed earlier, whether a “plain” char is treated as signed is implementation-defined.
Forward references: enumeration specifiers (3.5.2.2), structure and union specifiers (3.5.2.1).
When an unsigned integer is converted to another integral type, if the value can be represented by the new type, its value is unchanged.
When a signed integer is converted to an unsigned integer with equal or greater size, if the value of the signed integer is nonnegative, its value is unchanged. Otherwise: if the unsigned integer has greater size, the signed integer is first promoted to the signed integer corresponding to the unsigned integer; the value is converted to unsigned by adding to it one greater than the largest number that can be represented in the unsigned integer type.22
When an integer is demoted to an unsigned integer with smaller size, the result is the nonnegative remainder on division by the number one greater than the largest unsigned number that can be represented in the type with smaller size. When an integer is demoted to a signed integer with smaller size, or an unsigned integer is converted to its corresponding signed integer, if the value cannot be represented the result is implementation-defined.
When a value of floating type is converted to integral type, the fractional part is discarded. If the value of the integral part cannot be represented by the integral type, the behavior is undefined.23
When a value of integral type is converted to floating type, if the value being converted is in the range of values that can be represented but cannot be represented exactly, the result is either the nearest higher or nearest lower value, chosen in an implementation-defined manner.
When a float is promoted to double or long double, or a double is promoted to long double, its value is unchanged.
When a double is demoted to float or a long double to double or float, if the value being converted is outside the range of values that can be represented, the behavior is undefined. If the value being converted is in the range of values that can be represented but cannot be represented exactly, the result is either the nearest higher or nearest lower value, chosen in an implementation-defined manner.
Many binary operators that expect operands of arithmetic type cause conversions and yield result types in a similar way. The purpose is to yield a common type, which is also the type of the result. This pattern is called the usual arithmetic conversions: First, if either operand has type long double, the other operand is converted to long double. Otherwise, if either operand has type double, the other operand is converted to double. Otherwise, if either operand has type float, the other operand is converted to float. Otherwise, the integral promotions are performed on both operands. Then the following rules are applied: If either operand has type unsigned long int, the other operand is converted to unsigned long int. Otherwise, if one operand has type long int and the other has type unsigned int, if a long int can represent all values of an unsigned int, the operand of type unsigned int is converted to long int ; if a long int cannot represent all the values of an unsigned int, both operands are converted to unsigned long int. Otherwise, if either operand has type long int, the other operand is converted to long int. Otherwise, if either operand has type unsigned int, the other operand is converted to unsigned int. Otherwise, both operands have type int.
The values of operands and of the results of expressions may be represented in greater precision and range than that required by the type; the types are not changed thereby.
An lvalue is an expression (with an object type or an incomplete type other than void) that designates an object.24 When an object is said to have a particular type, the type is specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that does not have array type, does not have an incomplete type, does not have a const-qualified type, and if it is a structure or union, does not have any member (including, recursively, any member of all contained structures or unions) with a const-qualified type.
Except when it is the operand of the sizeof operator, the unary & operator, the ++ operator, the -- operator, or the left operand of the. operator or an assignment operator, an lvalue that does not have array type is converted to the value stored in the designated object (and is no longer an lvalue). If the lvalue has qualified type, the value has the unqualified version of the type of the lvalue; otherwise the value has the type of the lvalue. If the lvalue has an incomplete type and does not have array type, the behavior is undefined.
Except when it is the operand of the sizeof operator or the unary & operator, or is a character string literal used to initialize an array of character type, or is a wide string literal used to initialize an array with element type compatible with wchar_t, an lvalue that has type “array of type ” is converted to an expression that has type “pointer to type ” that points to the initial member of the array object and is not an lvalue.
A function designator is an expression that has function type. Except when it is the operand of the sizeof operator25 or the unary & operator, a function designator with type “function returning type ” is converted to an expression that has type “pointer to function returning type.”
Forward references: address and indirection operators (3.3.3.2),
assignment operators (3.3.16), common definitions <stddef.h>
(4.1.5), initialization (3.5.7), postfix increment and decrement
operators (3.3.2.4), prefix increment and decrement operators
(3.3.3.1), the sizeof operator (3.3.3.4), structure and union
members (3.3.2.3).
The (nonexistent) value of a void expression (an expression that has type void) shall not be used in any way, and implicit or explicit conversions (except to void ) shall not be applied to such an expression. If an expression of any other type occurs in a context where a void expression is required, its value or designator is discarded. (A void expression is evaluated for its side effects.)
A pointer to void may be converted to or from a pointer to any incomplete or object type. A pointer to any incomplete or object type may be converted to a pointer to void and back again; the result shall compare equal to the original pointer.
A pointer to a non-q-qualified type may be converted to a pointer to the q-qualified version of the type; the values stored in the original and converted pointers shall compare equal.
An integral constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant. If a null pointer constant is assigned to or compared for equality to a pointer, the constant is converted to a pointer of that type. Such a pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.
Two null pointers, converted through possibly different sequences of casts to pointer types, shall compare equal.
Forward references: cast operators (3.3.4), equality operators (3.3.9), simple assignment (3.3.16.1).
An expression is a sequence of operators and operands that specifies computation of a value, or that designates an object or a function, or that generates side effects, or that performs a combination thereof.
Between the previous and next sequence point an object shall have its stored value modified at most once by the evaluation of an expression. Furthermore, the prior value shall be accessed only to determine the value to be stored.26
Except as indicated by the syntax27 or otherwise specified later (for the function-call operator (), &&, ||, ?:, and comma operators), the order of evaluation of subexpressions and the order in which side effects take place are both unspecified.
Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, collectively described as bitwise operators )shall have operands that have integral type. These operators return values that depend on the internal representations of integers, and thus have implementation-defined aspects for signed types.
If an exception occurs during the evaluation of an expression (that is, if the result is not mathematically defined or not representable), the behavior is undefined.
An object shall have its stored value accessed only by an lvalue that has one of the following types:28
primary-expression: identifier constant string-literal ( expression )
An identifier is a primary expression, provided it has been declared as designating an object (in which case it is an lvalue) or a function (in which case it is a function designator).
A constant is a primary expression. Its type depends on its form, as detailed in 3.1.3.
A string literal is a primary expression. It is an lvalue with type as detailed in 3.1.4.
A parenthesized expression is a primary expression. Its type and value are identical to those of the unparenthesized expression. It is an lvalue, a function designator, or a void expression if the unparenthesized expression is, respectively, an lvalue, a function designator, or a void expression.
Forward references: declarations (3.5).
postfix-expression: primary-expression postfix-expression [ expression ] postfix-expression ( argument-expression-listopt ) postfix-expression . identifier postfix-expression -> identifier postfix-expression ++ postfix-expression --
argument-expression-list: assignment-expression argument-expression-list , assignment-expression
One of the expressions shall have type “pointer to object type,” the other expression shall have integral type, and the result has type “ type.”
A postfix expression followed by an expression in square brackets [] is a subscripted designation of a member of an array object. The definition of the subscript operator [] is that E1[E2] is identical to (*(E1+(E2))). Because of the conversion rules that apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the initial member of an array object) and E2 is an integer, E1[E2] designates the E2 -th member of E1 (counting from zero).
Successive subscript operators designate a member of a multi-dimensional array object. If E is an n -dimensional array ( n >=2) with dimensions i x j "x... x" k, then E (used as other than an lvalue) is converted to a pointer to an ( n -1)-dimensional array with dimensions j "x... x" k. If the unary * operator is applied to this pointer explicitly, or implicitly as a result of subscripting, the result is the pointed-to ( n -1)-dimensional array, which itself is converted into a pointer if used as other than an lvalue. It follows from this that arrays are stored in row-major order (last subscript varies fastest).
Consider the array object defined by the declaration
int x[3][5];
Here x is a 3x5 array of int s; more precisely, x is an array of three member objects, each of which is an array of five int s. In the expression x[i], which is equivalent to (*(x+(i))), x is first converted to a pointer to the initial array of five int s. Then i is adjusted according to the type of x, which conceptually entails multiplying i by the size of the object to which the pointer points, namely an array of five int objects. The results are added and indirection is applied to yield an array of five int s. When used in the expression x[i][j], that in turn is converted to a pointer to the first of the int s, so x[i][j] yields an int.
Forward references: additive operators (3.3.6), address and indirection operators (3.3.3.2), array declarators (3.5.4.2).
The expression that denotes the called
function29 shall have type
pointer to function returning void or returning an object type other
than array.
If the expression that denotes the called
function has a type that
includes a prototype, the number of arguments shall agree with the
number of parameters. Each argument shall have a type such that its
value may be assigned to an object with the unqualified version of the
type of its corresponding parameter.
A postfix expression followed by parentheses () containing a
possibly empty, comma-separated list of expressions is a function
call. The postfix expression denotes the called
function. The list
of expressions specifies the arguments to the function.
If the expression that precedes the parenthesized argument list in a function call consists solely of an identifier, and if no declaration is visible for this identifier, the identifier is implicitly declared exactly as if, in the innermost block containing the function call, the declaration
extern int identifier();
appeared.30
An argument may be an expression of any object type. In preparing for the call to a function, the arguments are evaluated, and each parameter is assigned the value of the corresponding argument.31 The value of the function call expression is specified in 3.6.6.4.
If the expression that denotes the called
function has a type that
does not include a prototype, the integral promotions are performed on
each argument and arguments that have type float are promoted to
double. These are called the default argument promotions. If the
number of arguments does not agree with the number of parameters, the
behavior is undefined. If the function is defined with a type that
does not include a prototype, and the types of the arguments after
promotion are not compatible with those of the parameters after
promotion, the behavior is undefined. If the function is defined with
a type that includes a prototype, and the types of the arguments after
promotion are not compatible with the types of the parameters, or if
the prototype ends with an ellipsis ( ",..." ), the behavior is
undefined.
If the expression that denotes the called
function has a type that
includes a prototype, the arguments are implicitly converted, as if by
assignment, to the types of the corresponding parameters. The
ellipsis notation in a function prototype declarator causes argument
type conversion to stop after the last declared parameter. The
default argument promotions are performed on trailing arguments. If
the function is defined with a type that is not compatible with the
type (of the expression) pointed to by the expression that denotes the
called function, the behavior is undefined.
No other conversions are performed implicitly; in particular, the number and types of arguments are not compared with those of the parameters in a function definition that does not include a function prototype declarator.
The order of evaluation of the function designator, the arguments, and subexpressions within the arguments is unspecified, but there is a sequence point before the actual call.
Recursive function calls shall be permitted, both directly and indirectly through any chain of other functions.
In the function call
(*pf[f1()]) (f2(), f3() + f4())
the functions f1, f2, f3, and f4 may be called in any order. All side effects shall be completed before the function pointed to by pf[f1()] is entered.
Forward references: function declarators (including prototypes) (3.5.4.3), function definitions (3.7.1), the return statement (3.6.6.4), simple assignment (3.3.16.1).
The first operand of the. operator shall have a qualified or unqualified structure or union type, and the second operand shall name a member of that type.
The first operand of the -> operator shall have type “pointer to qualified or unqualified structure” or “pointer to qualified or unqualified union,” and the second operand shall name a member of the type pointed to.
A postfix expression followed by a dot. and an identifier designates a member of a structure or union object. The value is that of the named member, and is an lvalue if the first expression is an lvalue. If the first expression has qualified type, the result has the so-qualified version of the type of the designated member.
A postfix expression followed by an arrow -> and an identifier designates a member of a structure or union object. The value is that of the named member of the object to which the first expression points, and is an lvalue.32 If the first expression is a pointer to a qualified type, the result has the so-qualified version of the type of the designated member.
With one exception, if a member of a union object is accessed after a value has been stored in a different member of the object, the behavior is implementation-defined.33 One special guarantee is made in order to simplify the use of unions: If a union contains several structures that share a common initial sequence, and if the union object currently contains one of these structures, it is permitted to inspect the common initial part of any of them. Two structures share a common initial sequence if corresponding members have compatible types for a sequence of one or more initial members.
If f is a function returning a structure or union, and x is a member of that structure or union, f().x is a valid postfix expression but is not an lvalue.
The following is a valid fragment:
union { struct { int alltypes; } n; struct { int type; int intnode; } ni; struct { int type; double doublenode; } nf; } u; /*...*/ u.nf.type = 1; u.nf.doublenode = 3.14; /*...*/ if (u.n.alltypes == 1) /*...*/ sin(u.nf.doublenode) /*...*/
Forward references: address and indirection operators (3.3.3.2), structure and union specifiers (3.5.2.1).
The operand of the postfix increment or decrement operator shall have qualified or unqualified scalar type and shall be a modifiable lvalue.
The result of the postfix ++ operator is the value of the operand. After the result is obtained, the value of the operand is incremented. (That is, the value 1 of the appropriate type is added to it.) See the discussions of additive operators and compound assignment for information on constraints, types and conversions and the effects of operations on pointers. The side effect of updating the stored value of the operand shall occur between the previous and the next sequence point.
The postfix -- operator is analogous to the postfix ++ operator, except that the value of the operand is decremented (that is, the value 1 of the appropriate type is subtracted from it).
Forward references: additive operators (3.3.6), compound assignment (3.3.16.2).
unary-expression: postfix-expression ++ unary-expression -- unary-expression unary-operator cast-expression sizeof unary-expression sizeof ( type-name )
unary-operator: one of & * + - ~ !
The operand of the prefix increment or decrement operator shall have qualified or unqualified scalar type and shall be a modifiable lvalue.
The value of the operand of the prefix ++ operator is incremented. The result is the new value of the operand after incrementation. The expression ++E is equivalent to (E+=1). See the discussions of additive operators and compound assignment for information on constraints, types, side effects, and conversions and the effects of operations on pointers.
The prefix -- operator is analogous to the prefix ++ operator, except that the value of the operand is decremented.
Forward references: additive operators (3.3.6), compound assignment (3.3.16.2).
The operand of the unary & operator shall be either a function designator or an lvalue that designates an object that is not a bit-field and is not declared with the register storage-class specifier.
The operand of the unary * operator shall have pointer type.
The result of the unary & (address-of) operator is a pointer to the object or function designated by its operand. If the operand has type “ type,” the result has type “pointer to type.”
The unary * operator denotes indirection. If the operand points to a function, the result is a function designator; if it points to an object, the result is an lvalue designating the object. If the operand has type “pointer to type,” the result has type “ type.” If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.34
Forward references: storage-class specifiers (3.5.1), structure and union specifiers (3.5.2.1).
The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, integral type; of the ! operator, scalar type.
The result of the unary + operator is the value of its operand. The integral promotion is performed on the operand, and the result has the promoted type.
The result of the unary - operator is the negative of its operand. The integral promotion is performed on the operand, and the result has the promoted type.
The result of the ~ operator is the bitwise complement of its
operand (that is, each bit in the result is set if and only if the
corresponding bit in the converted operand is not set). The integral
promotion is performed on the operand, and the result has the promoted
type. The expression ~E is equivalent to (ULONG_MAX-E) if E is
promoted to type unsigned long, to (UINT_MAX-E) if E is promoted to
type unsigned int. (The constants ULONG_MAX and UINT_MAX are defined
in the header <limits.h>
.)
The result of the logical negation operator ! is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. The expression !E is equivalent to (0==E).
Forward references: limits <float.h>
and <limits.h>
(4.1.4).
The sizeof operator shall not be applied to an expression that has function type or an incomplete type, to the parenthesized name of such a type, or to an lvalue that designates a bit-field object.
The sizeof operator yields the size (in bytes) of its operand, which may be an expression or the parenthesized name of a type. The size is determined from the type of the operand, which is not itself evaluated. The result is an integer constant.
When applied to an operand that has type char, unsigned char, or signed char, (or a qualified version thereof) the result is 1. When applied to an operand that has array type, the result is the total number of bytes in the array.35 When applied to an operand that has structure or union type, the result is the total number of bytes in such an object, including internal and trailing padding.
The value of the result is implementation-defined, and its type (an
unsigned integral type) is size_t defined in the <stddef.h>
header.
A principal use of the sizeof operator is in communication with routines such as storage allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to allocate and return a pointer to void. For example:
extern void *alloc(); double *dp = alloc(sizeof *dp);
The implementation of the alloc
function should ensure that its return
value is aligned suitably for conversion to a pointer to double.
Another use of the sizeof operator is to compute the number of members in an array:
sizeof array / sizeof array[0]
Forward references: common definitions <stddef.h>
(4.1.5),
declarations (3.5), structure and union specifiers (3.5.2.1), type
names (3.5.5).
cast-expression: unary-expression ( type-name ) cast-expression
Unless the type name specifies void type, the type name shall specify qualified or unqualified scalar type and the operand shall have scalar type.
Preceding an expression by a parenthesized type name converts the value of the expression to the named type. This construction is called a cast.36 A cast that specifies an implicit conversion or no conversion has no effect on the type or value of an expression.
Conversions that involve pointers (other than as permitted by the constraints of 3.3.16.1) shall be specified by means of an explicit cast; they have implementation-defined aspects: A pointer may be converted to an integral type. The size of integer required and the result are implementation-defined. If the space provided is not long enough, the behavior is undefined. An arbitrary integer may be converted to a pointer. The result is implementation-defined.37 A pointer to an object or incomplete type may be converted to a pointer to a different object type or a different incomplete type. The resulting pointer might not be valid if it is improperly aligned for the type pointed to. It is guaranteed, however, that a pointer to an object of a given alignment may be converted to a pointer to an object of the same alignment or a less strict alignment and back again; the result shall compare equal to the original pointer. (An object that has character type has the least strict alignment.) A pointer to a function of one type may be converted to a pointer to a function of another type and back again; the result shall compare equal to the original pointer. If a converted pointer is used to call a function that has a type that is not compatible with the type of the called function, the behavior is undefined.
Forward references: equality operators (3.3.9), function declarators (including prototypes) (3.5.4.3), simple assignment (3.3.16.1), type names (3.5.5).
multiplicative-expression: cast-expression multiplicative-expression * cast-expression multiplicative-expression / cast-expression multiplicative-expression % cast-expression
Each of the operands shall have arithmetic type. The operands of the % operator shall have integral type.
The usual arithmetic conversions are performed on the operands.
The result of the binary * operator is the product of the operands.
The result of the / operator is the quotient from the division of the first operand by the second; the result of the % operator is the remainder. In both operations, if the value of the second operand is zero, the behavior is undefined.
When integers are divided and the division is inexact, if both operands are positive the result of the / operator is the largest integer less than the algebraic quotient and the result of the % operator is positive. If either operand is negative, whether the result of the / operator is the largest integer less than the algebraic quotient or the smallest integer greater than the algebraic quotient is implementation-defined, as is the sign of the result of the % operator. If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a.
additive-expression: multiplicative-expression additive-expression + multiplicative-expression additive-expression - multiplicative-expression
For addition, either both operands shall have arithmetic type, or one operand shall be a pointer to an object type and the other shall have integral type. (Incrementing is equivalent to adding 1.)
For subtraction, one of the following shall hold:
If both operands have arithmetic type, the usual arithmetic conversions are performed on them.
The result of the binary + operator is the sum of the operands.
The result of the binary - operator is the difference resulting from the subtraction of the second operand from the first.
When an expression that has integral type is added to or subtracted from a pointer, the integral value is first multiplied by the size of the object pointed to. The result has the type of the pointer operand. If the pointer operand points to a member of an array object, and the array object is large enough, the result points to a member of the same array object, appropriately offset from the original member. Thus if P points to a member of an array object, the expression P+1 points to the next member of the array object. Unless both the pointer operand and the result point to a member of the same array object, or one past the last member of the array object, the behavior is undefined. Unless both the pointer operand and the result point to a member of the same array object, or the pointer operand points one past the last member of an array object and the result points to a member of the same array object, the behavior is undefined if the result is used as the operand of a unary * operator.
When two pointers to members of the same array object are
subtracted, the difference is divided by the size of a member. The
result represents the difference of the subscripts of the two array
members. The size of the result is implementation-defined, and its
type (a signed integral type) is ptrdiff_t defined in the <stddef.h>
header. As with any other arithmetic overflow, if the result does not
fit in the space provided, the behavior is undefined. If two pointers
that do not point to members of the same array object are subtracted,
the behavior is undefined. However, if P points either to a member of
an array object or one past the last member of an array object, and Q
points to the last member of the same array object, the expression
(Q+1) - P has the same value as (Q-P) + 1, even though Q+1 does not
point to a member of the array object.
Forward references: common definitions <stddef.h>
(4.1.5).
shift-expression: additive-expression shift-expression << additive-expression shift-expression >> additive-expression
Each of the operands shall have integral type.
The integral promotions are performed on each of the operands. The type of the result is that of the promoted left operand. If the value of the right operand is negative or is greater than or equal to the width in bits of the promoted left operand, the behavior is undefined.
The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated
bits are filled with zeros. If E1 has an unsigned type, the value of
the result is E1 multiplied by the quantity, 2 raised to the power E2,
reduced modulo ULONG_MAX+1 if E1 has type unsigned long, UINT_MAX+1
otherwise. (The constants ULONG_MAX and UINT_MAX are defined in the
header <limits.h>
.)
The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type or if E1 has a signed type and a nonnegative value, the value of the result is the integral part of the quotient of E1 divided by the quantity, 2 raised to the power E2. If E1 has a signed type and a negative value, the resulting value is implementation-defined.
relational-expression: shift-expression relational-expression < shift-expression relational-expression > shift-expression relational-expression <= shift-expression relational-expression >= shift-expression
One of the following shall hold:
If both of the operands have arithmetic type, the usual arithmetic conversions are performed.
When two pointers are compared, the result depends on the relative locations in the address space of the objects pointed to. If the objects pointed to are members of the same aggregate object, pointers to structure members declared later compare higher than pointers to members declared earlier in the structure, and pointers to array elements with larger subscript values compare higher than pointers to elements of the same array with lower subscript values. All pointers to members of the same union object compare equal. If the objects pointed to are not members of the same aggregate or union object, the result is undefined, with the following exception. If P points to the last member of an array object and Q points to a member of the same array object, the pointer expression P+1 compares higher than Q, even though P+1 does not point to a member of the array object.
Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.38 The result has type int.
equality-expression: relational-expression equality-expression == relational-expression equality-expression != relational-expression
One of the following shall hold:
The == (equal to) and the != (not equal to) operators are analogous to the relational operators except for their lower precedence.39
If two pointers to object or incomplete types compare equal, they
point to the same object. If two pointers to functions compare equal,
they point to the same
function. If two pointers point to the same
object or function, they compare equal.40 If one of the operands is
a pointer to an object or incomplete type and the other has type
pointer to a qualified or unqualified version of void, the pointer to
an object or incomplete type is converted to the type of the other
operand.
AND-expression: equality-expression AND-expression & equality-expression
Each of the operands shall have integral type.
The usual arithmetic conversions are performed on the operands.
The result of the binary & operator is the bitwise AND of the operands (that is, each bit in the result is set if and only if each of the corresponding bits in the converted operands is set).
exclusive-OR-expression: AND-expression exclusive-OR-expression ^ AND-expression
Each of the operands shall have integral type.
The usual arithmetic conversions are performed on the operands.
The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit in the result is set if and only if exactly one of the corresponding bits in the converted operands is set).
inclusive-OR-expression: exclusive-OR-expression inclusive-OR-expression | exclusive-OR-expression
Each of the operands shall have integral type.
The usual arithmetic conversions are performed on the operands.
The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in the result is set if and only if at least one of the corresponding bits in the converted operands is set).
logical-AND-expression: inclusive-OR-expression logical-AND-expression && inclusive-OR-expression
Each of the operands shall have scalar type.
The && operator shall yield 1 if both of its operands compare unequal to 0, otherwise it yields 0. The result has type int.
Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation; there is a sequence point after the evaluation of the first operand. If the first operand compares equal to 0, the second operand is not evaluated.
logical-OR-expression: logical-AND-expression logical-OR-expression || logical-AND-expression
Each of the operands shall have scalar type.
The || operator shall yield 1 if either of its operands compare unequal to 0, otherwise it yields 0. The result has type int.
Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; there is a sequence point after the evaluation of the first operand. If the first operand compares unequal to 0, the second operand is not evaluated.
conditional-expression: logical-OR-expression logical-OR-expression ? expression : conditional-expression
The first operand shall have scalar type.
One of the following shall hold for the second and third operands:
The first operand is evaluated; there is a sequence point after its evaluation. The second operand is evaluated only if the first compares unequal to 0; the third operand is evaluated only if the first compares equal to 0; the value of the second or third operand (whichever is evaluated) is the result.41
If both the second and third operands have arithmetic type, the usual arithmetic conversions are performed to bring them to a common type and the result has that type. If both the operands have structure or union type, the result has that type. If both operands have void type, the result has void type.
If both the second and third operands are pointers or one is a null pointer constant and the other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers of the types pointed-to by both operands. Furthermore, if both operands are pointers to compatible types or differently qualified versions of a compatible type, the result has the composite type; if one operand is a null pointer constant, the result has the type of the other operand; otherwise, one operand is a pointer to void or a qualified version of void, in which case the other operand is converted to type pointer to void, and the result has that type.
assignment-expression: conditional-expression unary-expression assignment-operator assignment-expression
assignment-operator: one of = *= /= %= += -= <<= >>= &= ^= |=
An assignment operator shall have a modifiable lvalue as its left operand.
An assignment operator stores a value in the object designated by the left operand. An assignment expression has the value of the left operand after the assignment, but is not an lvalue. The type of an assignment expression is the type of the left operand unless the left operand has qualified type, in which case it is the unqualified version of the type of the left operand. The side effect of updating the stored value of the left operand shall occur between the previous and the next sequence point.
The order of evaluation of the operands is unspecified.
One of the following shall hold:42
In simple assignment ( = ), the value of the right operand is converted to the type of the assignment expression and replaces the value stored in the object designated by the left operand.
If the value being stored in an object is accessed from another object that overlaps in any way the storage of the first object, then the overlap shall be exact and the two objects shall have qualified or unqualified versions of a compatible type; otherwise the behavior is undefined.
In the program fragment
int f(void); char c; /*...*/ /*...*/ ((c = f()) == -1) /*...*/
the int value returned by the function may be truncated when stored in the char, and then converted back to int width prior to the comparison. In an implementation in which “plain” char has the same range of values as unsigned char (and char is narrower than int ), the result of the conversion cannot be negative, so the operands of the comparison can never compare equal. Therefore, for full portability the variable c should be declared as int.
For the operators += and -= only, either the left operand shall be a pointer to an object type and the right shall have integral type, or the left operand shall have qualified or unqualified arithmetic type and the right shall have arithmetic type.
For the other operators, each operand shall have arithmetic type consistent with those allowed by the corresponding binary operator.
A compound assignment of the form E1 op = E2 differs from the simple assignment expression E1 = E1 op (E2) only in that the lvalue E1 is evaluated only once.
expression: assignment-expression expression , assignment-expression
The left operand of a comma operator is evaluated as a void expression; there is a sequence point after its evaluation. Then the right operand is evaluated; the result has its type and value.43
As indicated by the syntax, in contexts where a comma is a punctuator (in lists of arguments to functions and lists of initializers) the comma operator as described in this section cannot appear. On the other hand, it can be used within a parenthesized expression or within the second expression of a conditional operator in such contexts. In the function call
f(a, (t=3, t+2), c)
the function has three arguments, the second of which has the value 5.
Forward references: initialization (3.5.7).
constant-expression: conditional-expression
A constant expression can be evaluated during translation rather than runtime, and accordingly may be used in any place that a constant may be.
Constant expressions shall not contain assignment, increment, decrement, function-call, or comma operators, except when they are contained within the operand of a sizeof operator.44
Each constant expression shall evaluate to a constant that is in the range of representable values for its type.
An expression that evaluates to a constant is required in several contexts.45 If the expression is evaluated in the translation environment, the arithmetic precision and range shall be at least as great as if the expression were being evaluated in the execution environment.
An integral constant expression shall have integral type and shall only have operands that are integer constants, enumeration constants, character constants, sizeof expressions, and floating constants that are the immediate operands of casts. Cast operators in an integral constant expression shall only convert arithmetic types to integral types, except as part of an operand to the sizeof operator.
More latitude is permitted for constant expressions in initializers. Such a constant expression shall evaluate to one of the following:
An arithmetic constant expression shall have arithmetic type and shall only have operands that are integer constants, floating constants, enumeration constants, character constants, and sizeof expressions. Cast operators in an arithmetic constant expression shall only convert arithmetic types to arithmetic types, except as part of an operand to the sizeof operator.
An address constant is a pointer to an lvalue designating an object of static storage duration, or to a function designator; it shall be created explicitly, using the unary & operator, or implicitly, by the use of an expression of array or function type. The array-subscript [] and member-access. and -> operators, the address & and indirection * unary operators, and pointer casts may be used in the creation an address constant, but the value of an object shall not be accessed by use of these operators.
The semantic rules for the evaluation of a constant expression are the same as for non-constant expressions.46
Forward references: initialization (3.5.7).
declaration: declaration-specifiers init-declarator-listopt ;
declaration-specifiers: storage-class-specifier declaration-specifiersopt type-specifier declaration-specifiersopt type-qualifier declaration-specifiersopt
init-declarator-list: init-declarator init-declarator-list , init-declarator
init-declarator: declarator declarator = initializer
A declaration shall declare at least a declarator, a tag, or the members of an enumeration.
If an identifier has no linkage, there shall be no more than one declaration of the identifier (in a declarator or type specifier) with the same scope and in the same name space, except for tags as specified in 3.5.2.3.
All declarations in the same scope that refer to the same object or function shall specify compatible types.
A declaration specifies the interpretation and attributes of a set of identifiers. A declaration that also causes storage to be reserved for an object or function named by an identifier is a definition.47
The declaration specifiers consist of a sequence of specifiers that indicate the linkage, storage duration, and part of the type of the entities that the declarators denote. The init-declarator-list is a comma-separated sequence of declarators, each of which may have additional type information, or an initializer, or both. The declarators contain the identifiers (if any) being declared.
If an identifier for an object is declared with no linkage, the type for the object shall be complete by the end of its declarator, or by the end of its init-declarator if it has an initializer.
Forward references: declarators (3.5.4), enumeration specifiers (3.5.2.2), initialization (3.5.7), tags (3.5.2.3).
storage-class-specifier: typedef extern static auto register
At most one storage-class specifier may be given in the declaration specifiers in a declaration.48
The typedef specifier is called a “storage-class specifier” for syntactic convenience only; it is discussed in 3.5.6. The meanings of the various linkages and storage durations were discussed in 3.1.2.2 and 3.1.2.4.
A declaration of an identifier for an object with storage-class specifier register suggests that access to the object be as fast as possible. The extent to which such suggestions are effective is implementation-defined.49
The declaration of an identifier for a function that has block scope shall have no explicit storage-class specifier other than extern.
Forward references: type definitions (3.5.6).
type-specifier: void char short int long float double signed unsigned struct-or-union-specifier enum-specifier typedef-name
Each list of type specifiers shall be one of the following sets; the type specifiers may occur in any order, possibly intermixed with the other declaration specifiers.
Specifiers for structures, unions, and enumerations are discussed in 3.5.2.1 through 3.5.2.3. Declarations of typedef names are discussed in 3.5.6. The characteristics of the other types are discussed in 3.1.2.5.
Each of the above comma-separated lists designates the same type, except that for bit-field declarations, signed int (or signed ) may differ from int (or no type specifiers).
Forward references: enumeration specifiers (3.5.2.2), structure and union specifiers (3.5.2.1), tags (3.5.2.3), type definitions (3.5.6).
struct-or-union-specifier: struct-or-union identifieropt { struct-declaration-list } struct-or-union identifier
struct-or-union: struct union
struct-declaration-list: struct-declaration struct-declaration-list struct-declaration
struct-declaration: specifier-qualifier-list struct-declarator-list ;
specifier-qualifier-list: type-specifier specifier-qualifier-listopt type-qualifier specifier-qualifier-listopt
struct-declarator-list: struct-declarator struct-declarator-list , struct-declarator
struct-declarator: declarator declaratoropt : constant-expression
A structure or union shall not contain a member with incomplete or function type. Hence it shall not contain an instance of itself (but may contain a pointer to an instance of itself).
The expression that specifies the width of a bit-field shall be an integral constant expression that has nonnegative value that shall not exceed the number of bits in an ordinary object of compatible type. If the value is zero, the declaration shall have no declarator.
As discussed in 3.1.2.5, a structure is a type consisting of a sequence of named members, whose storage is allocated in an ordered sequence, and a union is a type consisting of a sequence of named members, whose storage overlap.
Structure and union specifiers have the same form.
The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type, within a translation unit. The struct-declaration-list is a sequence of declarations for the members of the structure or union. The type is incomplete until after the } that terminates the list.
A member of a structure or union may have any object type. In addition, a member may be declared to consist of a specified number of bits (including a sign bit, if any). Such a member is called a bit-field ;50 its width is preceded by a colon.
A bit-field may have type int, unsigned int, or signed int. Whether the high-order bit position of a “plain” int bit-field is treated as a sign bit is implementation-defined. A bit-field is interpreted as an integral type consisting of the specified number of bits.
An implementation may allocate any addressable storage unit large enough to hold a bit-field. If enough space remains, a bit-field that immediately follows another bit-field in a structure shall be packed into adjacent bits of the same unit. If insufficient space remains, whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is implementation-defined. The order of allocation of bit-fields within a unit (high-order to low-order or low-order to high-order) is implementation-defined. The alignment of the addressable storage unit is unspecified.
A bit-field declaration with no declarator, but only a colon and a width, indicates an unnamed bit-field.51 As a special case of this, a bit-field with a width of 0 indicates that no further bit-field is to be packed into the unit in which the previous bit-field, if any, was placed.
Each non-bit-field member of a structure or union object is aligned in an implementation-defined manner appropriate to its type.
Within a structure object, the non-bit-field members and the units in which bit-fields reside have addresses that increase in the order in which they are declared. A pointer to a structure object, suitably cast, points to its initial member (or if that member is a bit-field, then to the unit in which it resides), and vice versa. There may therefore be unnamed holes within a structure object, but not at its beginning, as necessary to achieve the appropriate alignment.
The size of a union is sufficient to contain the largest of its members. The value of at most one of the members can be stored in a union object at any time. A pointer to a union object, suitably cast, points to each of its members (or if a member is a bit-field, then to the unit in which it resides), and vice versa.
There may also be unnamed padding at the end of a structure or union, as necessary to achieve the appropriate alignment were the structure or union to be a member of an array.
enum-specifier: enum identifieropt { enumerator-list } enum identifier
enumerator-list: enumerator enumerator-list , enumerator
enumerator: enumeration-constant enumeration-constant = constant-expression
The expression that defines the value of an enumeration constant shall be an integral constant expression that has a value representable as an int.
The identifiers in an enumerator list are declared as constants that have type int and may appear wherever such are permitted.52 An enumerator with = defines its enumeration constant as the value of the constant expression. If the first enumerator has no =, the value of its enumeration constant is 0. Each subsequent enumerator with no = defines its enumeration constant as the value of the constant expression obtained by adding 1 to the value of the previous enumeration constant. (A combination of both forms of enumerators may produce enumeration constants with values that duplicate other values in the same enumeration.) The enumerators of an enumeration are also known as its members.
Each enumerated type shall be compatible with an integer type; the choice of type is implementation-defined.
enum hue { chartreuse, burgundy, claret=20, winedark }; /*...*/ enum hue col, *cp; /*...*/ col = claret; cp = &col; /*...*/ /*...*/ (*cp != burgundy) /*...*/
makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a pointer to an object that has that type. The enumerated values are in the set {0, 1, 20, 21}.
A type specifier of the form
struct-or-union identifier { struct-declaration-list } enum identifier { enumerator-list }
declares the identifier to be the tag of the structure, union, or enumeration specified by the list. The list defines the structure content,union content,or enumeration content.If this declaration of the tag is visible, a subsequent declaration that uses the tag and that omits the bracketed list specifies the declared structure, union, or enumerated type. Subsequent declarations in the same scope shall omit the bracketed list.
If a type specifier of the form
occurs prior to the declaration that defines the content, the structure or union is an incomplete type.53 It declares a tag that specifies a type that may be used only when the size of an object of the specified type is not needed.54 If the type is to be completed, another declaration of the tag in the same scope (but not in an enclosed block, which declares a new type known only within that block) shall define the content. A declaration of the form
specifies a structure or union type and declares a tag, both visible only within the scope in which the declaration occurs. It specifies a new type distinct from any type with the same tag in an enclosing scope (if any).
A type specifier of the form
struct-or-union { struct-declaration-list } enum { enumerator-list }
specifies a new structure, union, or enumerated type, within the translation unit, that can only be referred to by the declaration of which it is a part.55
This mechanism allows declaration of a self-referential structure.
struct tnode { int count; struct tnode *left, *right; };
specifies a structure that contains an integer and two pointers to objects of the same type. Once this declaration has been given, the declaration
struct tnode s, *sp;
declares s to be an object of the given type and sp to be a pointer to an object of the given type. With these declarations, the expression sp->left refers to the left struct tnode pointer of the object to which sp points; the expression s.right->count designates the count member of the right struct tnode pointed to from s.
The following alternative formulation uses the typedef mechanism:
typedef struct tnode TNODE; struct tnode { int count; TNODE *left, *right; }; TNODE s, *sp;
To illustrate the use of prior declaration of a tag to specify a pair of mutually-referential structures, the declarations
struct s1 { struct s2 *s2p; /*...*/ }; /* D1 */ struct s2 { struct s1 *s1p; /*...*/ }; /* D2 */
specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in D2. To eliminate this context sensitivity, the otherwise vacuous declaration
struct s2;
may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then completes the specification of the new type.
Forward references: type definitions (3.5.6).
type-qualifier: const volatile
The same type qualifier shall not appear more than once in the same specifier list or qualifier list, either directly or via one or more typedef s.
The properties associated with qualified types are meaningful only for expressions that are lvalues.56
If an attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is made to refer to an object defined with a volatile-qualified type through use of an lvalue with non-volatile-qualified type, the behavior is undefined.57
An object that has volatile-qualified type may be modified in ways unknown to the implementation or have other unknown side effects. Therefore any expression referring to such an object shall be evaluated strictly according to the rules of the abstract machine, as described in 2.1.2.3. Furthermore, at every sequence point the value last stored in the object shall agree with that prescribed by the abstract machine, except as modified by the unknown factors mentioned previously.58 What constitutes an access to an object that has volatile-qualified type is implementation-defined.
If the specification of an array type includes any type qualifiers, the element type is so-qualified, not the array type. If the specification of a function type includes any type qualifiers, the behavior is undefined.59
For two qualified types to be compatible, both shall have the identically qualified version of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers does not affect the specified type.
An object declared
extern const volatile int real_time_clock;
may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.
The following declarations and expressions illustrate the behavior when type qualifiers modify an aggregate type:
const struct s { int mem; } cs = { 1 }; struct s ncs; /* the object ncs is modifiable */ typedef int A[2][3]; const A a = {{4, 5, 6}, {7, 8, 9}}; /* array of array of const int */ int *pi; const int *pci;
ncs = cs; /* valid */ cs = ncs; /* violates modifiable lvalue constraint for = */ pi = &ncs.mem; /* valid */ pi = &cs.mem; /* violates type constraints for = */ pci = &cs.mem; /* valid */ pi = a[0]; /* invalid: a[0] has type “const int * ” */
declarator: pointeropt direct-declarator
direct-declarator: identifier ( declarator ) direct-declarator [ constant-expressionopt ] direct-declarator ( parameter-type-list ) direct-declarator ( identifier-listopt )
pointer: * type-qualifier-listopt * type-qualifier-listopt pointer
type-qualifier-list: type-qualifier type-qualifier-list type-qualifier
parameter-type-list: parameter-list parameter-list , ...
parameter-list: parameter-declaration parameter-list , parameter-declaration
parameter-declaration: declaration-specifiers declarator declaration-specifiers abstract-declaratoropt
identifier-list: identifier identifier-list , identifier
Each declarator declares one identifier, and asserts that when an operand of the same form as the declarator appears in an expression, it designates a function or object with the scope, storage duration, and type indicated by the declaration specifiers.
In the following subsections, consider a declaration
T D1
where T contains the declaration specifiers that specify a type T (such as int) and D1 is a declarator that contains an identifier ident. The type specified for the identifier ident in the various forms of declarator is described inductively using this notation.
If, in the declaration “ T D1,” D1 has the form
then the type specified for ident is T.
If, in the declaration “ T D1,” D1 has the form
( D )
then ident has the type specified by the declaration “ T D.” Thus, a declarator in parentheses is identical to the unparenthesized declarator, but the binding of complex declarators may be altered by parentheses.
The implementation shall allow the specification of types that have at least 12 pointer, array, and function declarators (in any valid combinations) modifying an arithmetic, a structure, a union, or an incomplete type, either directly or via one or more typedef s.
Forward references: type definitions (3.5.6).
If, in the declaration “ T D1,” D1 has the form
* type-qualifier-listopt D
and the type specified for ident in the declaration “ T D ” is “ "derived-declarator-type-list T",” then the type specified for ident is “ "derived-declarator-type-list type-qualifier-list" pointer to T.” For each type qualifier in the list, ident is a so-qualified pointer.
For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types.
The following pair of declarations demonstrates the difference between a “variable pointer to a constant value” and a “constant pointer to a variable value.”
const int *ptr_to_constant; int *const constant_ptr;
The contents of the const int pointed to by ptr_to_constant shall not be modified, but ptr_to_constant itself may be changed to point to another const int. Similarly, the contents of the int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the same location.
The declaration of the constant pointer constant_ptr may be clarified by including a definition for the type “pointer to int.”
typedef int *int_ptr; const int_ptr constant_ptr;
declares constant_ptr as an object that has type “const-qualified pointer to int.”
The expression that specifies the size of an array shall be an integral constant expression that has a value greater than zero.
If, in the declaration “ T D1,” D1 has the form
D[ constant-expressionopt ]
and the type specified for ident in the declaration “ T D ” is “ "derived-declarator-type-list T",” then the type specified for ident is “ derived-declarator-type-list array of T.”60 If the size is not present, the array type is an incomplete type.
For two array types to be compatible, both shall have compatible element types, and if both size specifiers are present, they shall have the same value.
float fa[11], *afp[17];
declares an array of float numbers and an array of pointers to float numbers.
Note the distinction between the declarations
extern int *x; extern int y[];
The first declares x to be a pointer to int ; the second declares y to be an array of int of unspecified size (an incomplete type), the storage for which is defined elsewhere.
Forward references: function definitions (3.7.1), initialization (3.5.7).
A function declarator shall not specify a return type that is a function type or an array type.
The only storage-class specifier that shall occur in a parameter declaration is register.
An identifier list in a function declarator that is not part of a function definition shall be empty.
If, in the declaration “ T D1,” D1 has the form
D( parameter-type-list ) D( identifier-listopt )
and the type specified for ident in the declaration “ T D ” is “ "derived-declarator-type-list T",” then the type specified for ident is “ derived-declarator-type-list function returning T.”
A parameter type list specifies the types of, and may declare identifiers for, the parameters of the function. If the list terminates with an ellipsis (,... ), no information about the number or types of the parameters after the comma is supplied.61 The special case of void as the only item in the list specifies that the function has no parameters.
In a parameter declaration, a single typedef name in parentheses is taken to be an abstract declarator that specifies a function with a single parameter, not as redundant parentheses around the identifier for a declarator.
The storage-class specifier in the declaration specifiers for a parameter declaration, if present, is ignored unless the declared parameter is one of the members of the parameter type list for a function definition.
An identifier list declares only the identifiers of the parameters of the function. An empty list in a function declarator that is part of a function definition specifies that the function has no parameters. The empty list in a function declarator that is not part of a function definition specifies that no information about the number or types of the parameters is supplied.62
For two function types to be compatible, both shall specify compatible return types.63 Moreover, the parameter type lists, if both are present, shall agree in the number of parameters and in use of the ellipsis terminator; corresponding parameters shall have compatible types. If one type has a parameter type list and the other type is specified by a function declarator that is not part of a function definition and that contains an empty identifier list, the parameter list shall not have an ellipsis terminator and the type of each parameter shall be compatible with the type that results from the application of the default argument promotions. If one type has a parameter type list and the other type is specified by a function definition that contains a (possibly empty) identifier list, both shall agree in the number of parameters, and the type of each prototype parameter shall be compatible with the type that results from the application of the default argument promotions to the type of the corresponding identifier. (For each parameter declared with function or array type, its type for these comparisons is the one that results from conversion to a pointer type, as in 3.7.1. For each parameter declared with qualified type, its type for these comparisons is the unqualified version of its declared type.)
The declaration
int f(void), *fip(), (*pfi)();
declares a function f with no parameters returning an int, a function fip with no parameter specification returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the declaration suggests, and the same construction in an expression requires, the calling of a function fip, and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function designator, which is then used to call the function; it returns an int.
If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the declaration occurs inside a function, the identifiers of the functions f and fip have block scope and external linkage, and the identifier of the pointer pfi has block scope and no linkage.
Here are two more intricate examples.
int (*apfi[3])(int *x, int *y);
declares an array apfi of three pointers to functions returning int. Each of these functions has two parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and go out of scope at the end of the declaration of apfi. The declaration
int (*fpfi(int (*)(long), int))(int, ...);
declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two parameters: a pointer to a function returning an int (with one parameter of type long ), and an int. The pointer returned by fpfi points to a function that has at least one parameter, which has type int.
Forward references: function definitions (3.7.1), type names (3.5.5).
type-name: specifier-qualifier-list abstract-declaratoropt
abstract-declarator: pointer pointeropt direct-abstract-declarator
direct-abstract-declarator: ( abstract-declarator ) direct-abstract-declaratoropt [ constant-expressionopt ] direct-abstract-declaratoropt ( parameter-type-listopt )
In several contexts it is desired to specify a type. This is accomplished using a type name, which is syntactically a declaration for a function or an object of that type that omits the identifier.64
The constructions
(a) int (b) int * (c) int *[3] (d) int (*)[3] (e) int *() (f) int (*)(void) (g) int (*const [])(unsigned int, ...)
name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an array of three int's, (e) function with no parameter specification returning a pointer to int, (f) pointer to function with no parameters returning an int, and (g) array of an unspecified number of constant pointers to functions, each with one parameter that has type unsigned int and an unspecified number of other parameters, returning an int.
In a declaration whose storage-class specifier is typedef, each declarator defines an identifier to be a typedef name that specifies the type specified for the identifier in the way described in 3.5.4. A typedef declaration does not introduce a new type, only a synonym for the type so specified. That is, in the following declarations:
typedef T type_ident; type_ident D;
type_ident is defined as a typedef name with the type specified by the declaration specifiers in T (known as T ), and the identifier in D has the type “ "derived-declarator-type-list T" ” where the derived-declarator-type-list is specified by the declarators of D. A typedef name shares the same name space as other identifiers declared in ordinary declarators. If the identifier is redeclared in an inner scope or is declared as a member of a structure or union in the same or an inner scope, the type specifiers shall not be omitted in the inner declaration.
After
typedef int MILES, KLICKSP(); typedef struct { double re, im; } complex;
the constructions
MILES distance; extern KLICKSP *metricp; complex x; complex z, *zp;
are all valid declarations. The type of distance is int, that of metricp is “pointer to function with no parameter specification returning int,” and that of x and z is the specified structure; zp is a pointer to such a structure. The object distance has a type compatible with any other int object.
After the declarations
typedef struct s1 { int x; } t1, *tp1; typedef struct s2 { int x; } t2, *tp2;
type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, and int.
The following constructions
typedef signed int t; typedef int plain; struct tag { unsigned t:4; const t:5; plain r:5; };
declare a typedef name t with type signed int, a typedef name plain with type int, and a structure with three bit-field members, one named t that contains values in the range [0,15], an unnamed const-qualified bit-field which (if it could be accessed) would contain values in at least the range [-15,+15], and one named r that contains values in the range [0,31] or values in at least the range [-15,+15]. (The choice of range is implementation-defined.) If these declarations are followed in an inner scope by
t f(t (t)); long t;
then a function f is declared with type “function returning signed int with one unnamed parameter with type pointer to function returning signed int with one unnamed parameter with type signed int,” and an identifier t with type long.
initializer: assignment-expression { initializer-list } { initializer-list , }
initializer-list: initializer initializer-list , initializer
There shall be no more initializers in an initializer list than there are objects to be initialized.
The type of the entity to be initialized shall be an object type or an array of unknown size.
All the expressions in an initializer for an object that has static storage duration or in an initializer list for an object that has aggregate or union type shall be constant expressions.
If the declaration of an identifier has block scope, and the identifier has external or internal linkage, there shall be no initializer for the identifier.
An initializer specifies the initial value stored in an object.
All unnamed structure or union members are ignored during initialization.
If an object that has static storage duration is not initialized explicitly, it is initialized implicitly as if every member that has arithmetic type were assigned 0 and every member that has pointer type were assigned a null pointer constant. If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate.65
The initializer for a scalar shall be a single expression, optionally enclosed in braces. The initial value of the object is that of the expression; the same type constraints and conversions as for simple assignment apply.
A brace-enclosed initializer for a union object initializes the member that appears first in the declaration list of the union type.
The initializer for a structure or union object that has automatic storage duration either shall be an initializer list as described below, or shall be a single expression that has compatible structure or union type. In the latter case, the initial value of the object is that of the expression.
The rest of this section deals with initializers for objects that have aggregate or union type.
An array of character type may be initialized by a character string literal, optionally enclosed in braces. Successive characters of the character string literal (including the terminating null character if there is room or if the array is of unknown size) initialize the members of the array.
An array with element type compatible with wchar_t may be initialized by a wide string literal, optionally enclosed in braces. Successive codes of the wide string literal (including the terminating zero-valued code if there is room or if the array is of unknown size) initialize the members of the array.
Otherwise, the initializer for an object that has aggregate type shall be a brace-enclosed list of initializers for the members of the aggregate, written in increasing subscript or member order; and the initializer for an object that has union type shall be a brace-enclosed initializer for the first member of the union.
If the aggregate contains members that are aggregates or unions, or if the first member of a union is an aggregate or union, the rules apply recursively to the subaggregates or contained unions. If the initializer of a subaggregate or contained union begins with a left brace, the initializers enclosed by that brace and its matching right brace initialize the members of the subaggregate or the first member of the contained union. Otherwise, only enough initializers from the list are taken to account for the members of the first subaggregate or the first member of the contained union; any remaining initializers are left to initialize the next member of the aggregate of which the current subaggregate or contained union is a part.
If there are fewer initializers in a list than there are members of an aggregate, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.
If an array of unknown size is initialized, its size is determined by the number of initializers provided for its members. At the end of its initializer list, the array no longer has incomplete type.
The declaration
int x[] = { 1, 3, 5 };
defines and initializes x as a one-dimensional array object that has three members, as no size was specified and there are three initializers.
float y[4][3] = { { 1, 3, 5 }, { 2, 4, 6 }, { 3, 5, 7 }, };
is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of the array object y[0], namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have been achieved by
float y[4][3] = { 1, 3, 5, 2, 4, 6, 3, 5, 7 };
The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the next three are taken successively for y[1] and y[2]. Also,
float z[4][3] = { { 1 }, { 2 }, { 3 }, { 4 } };
initializes the first column of z as specified and initializes the rest with zeros.
struct { int a[3], b; } w[] = { { 1 }, 2 };
is a definition with an inconsistently bracketed initialization. It defines an array with two member structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
The declaration
short q[4][3][2] = { { 1 }, { 2, 3 }, { 4, 5, 6 } };
contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for q[0][0][0] does not begin with a left brace, so up to six items from the current list may be used. There is only one, so the values for the remaining five members are initialized with zero. Likewise, the initializers for q[1][0][0] and q[2][0][0] do not begin with a left brace, so each uses up to six items, initializing their respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a diagnostic message would occur. The same initialization result could have been achieved by:
short q[4][3][2] = { 1, 0, 0, 0, 0, 0, 2, 3, 0, 0, 0, 0, 4, 5, 6 };
or by:
short q[4][3][2] = { { { 1 }, }, { { 2, 3 }, }, { { 4, 5 }, { 6 }, } };
in a fully-bracketed form.
Note that the fully-bracketed and minimally-bracketed forms of initialization are, in general, less likely to cause confusion.
Finally, the declaration
char s[] = "abc", t[3] = "abc";
defines “plain” char array objects s and t whose members are initialized with character string literals. This declaration is identical to
char s[] = { 'a', 'b', 'c', '\0' }, t[] = { 'a', 'b', 'c' };
The contents of the arrays are modifiable. On the other hand, the declaration
char *p = "abc";
defines p with type “pointer to char ” that is initialized to point to an object with type “array of char ” whose members are initialized with a character string literal. If an attempt is made to use p to modify the contents of the array, the behavior is undefined.
Forward references: common definitions <stddef.h>
(4.1.5).
statement: labeled-statement compound-statement expression-statement selection-statement iteration-statement jump-statement
A statement specifies an action to be performed. Except as indicated, statements are executed in sequence.
A full expression is an expression that is not part of another expression. Each of the following is a full expression: an initializer; the expression in an expression statement; the controlling expression of a selection statement ( if or switch ); the controlling expression of a while or do statement; each of the three expressions of a for statement; the expression in a return statement. The end of a full expression is a sequence point.
Forward references: expression and null statements (3.6.3), selection statements (3.6.4), iteration statements (3.6.5), the return statement (3.6.6.4).
labeled-statement: identifier : statement case constant-expression : statement default : statement
A case or default label shall appear only in a switch statement. Further constraints on such labels are discussed under the switch statement.
Any statement may be preceded by a prefix that declares an identifier as a label name. Labels in themselves do not alter the flow of control, which continues unimpeded across them.
Forward references: the goto statement (3.6.6.1), the switch statement (3.6.4.2).
compound-statement: { declaration-listopt statement-listopt }
declaration-list: declaration declaration-list declaration
statement-list: statement statement-list statement
A compound statement (also called a block )allows a set of statements to be grouped into one syntactic unit, which may have its own set of declarations and initializations (as discussed in 3.1.2.4). The initializers of objects that have automatic storage duration are evaluated and the values are stored in the objects in the order their declarators appear in the translation unit.
expression-statement: expressionopt ;
The expression in an expression statement is evaluated as a void expression for its side effects.66
A null statement (consisting of just a semicolon) performs no operations.
If a function call is evaluated as an expression statement for its side effects only, the discarding of its value may be made explicit by converting the expression to a void expression by means of a cast:
int p(int); /*...*/ (void)p(0);
In the program fragment
char *s; /*...*/ while (*s++ != '\0') ;
a null statement is used to supply an empty loop body to the iteration statement.
A null statement may also be used to carry a label just before the closing } of a compound statement.
while (loop1) { /*...*/ while (loop2) { /*...*/ if (want_out) goto end_loop1; /*...*/ } /*...*/ end_loop1: ; }
Forward references: iteration statements (3.6.5).
selection-statement: if ( expression ) statement if ( expression ) statement else statement switch ( expression ) statement
A selection statement selects among a set of statements depending on the value of a controlling expression.
The controlling expression of an if statement shall have scalar type.
In both forms, the first substatement is executed if the expression compares unequal to 0. In the else form, the second substatement is executed if the expression compares equal to 0. If the first substatement is reached via a label, the second substatement is not executed.
An else is associated with the lexically immediately preceding else -less if that is in the same block (but not in an enclosed block).
The controlling expression of a switch statement shall have integral type. The expression of each case label shall be an integral constant expression. No two of the case constant expressions in the same switch statement shall have the same value after conversion. There may be at most one default label in a switch statement. (Any enclosed switch statement may have a default label or case constant expressions with values that duplicate case constant expressions in the enclosing switch statement.)
A switch statement causes control to jump to, into, or past the statement that is the switch body, depending on the value of a controlling expression, and on the presence of a default label and the values of any case labels on or in the switch body. A case or default label is accessible only within the closest enclosing switch statement.
The integral promotions are performed on the controlling expression. The constant expression in each case label is converted to the promoted type of the controlling expression. If a converted value matches that of the promoted controlling expression, control jumps to the statement following the matched case label. Otherwise, if there is a default label, control jumps to the labeled statement. If no converted case constant expression matches and there is no default label, no part of the switch body is executed.
As discussed previously (2.2.4.1), the implementation may limit the number of case values in a switch statement.
iteration-statement: while ( expression ) statement do statement while ( expression ) ; for ( expressionopt ; expressionopt ; expressionopt ) statement
The controlling expression of an iteration statement shall have scalar type. Semantics
An iteration statement causes a statement called the loop body to be executed repeatedly until the controlling expression compares equal to 0.
The evaluation of the controlling expression takes place before each execution of the loop body.
The evaluation of the controlling expression takes place after each execution of the loop body.
Except for the behavior of a continue statement in the loop body, the statement
for ( expression-1 ; expression-2 ; expression-3 ) statement
and the sequence of statements
expression-1 ; while ( expression-2) { statement expression-3 ; }
are equivalent.67 expression-1 expression-2, expression-3
Both expression-1 and expression-3 may be omitted. Each is evaluated as a void expression. An omitted expression-2 is replaced by a nonzero constant.
Forward references: the continue statement (3.6.6.2).
jump-statement: goto identifier ; continue ; break ; return expressionopt ;
A jump statement causes an unconditional jump to another place.
The identifier in a goto statement shall name a label located
somewhere in the current
function.
A goto statement causes an unconditional jump to the statement
prefixed by the named label in the current
function.
A continue statement shall appear only in or as a loop body.
A continue statement causes a jump to the loop-continuation portion of the smallest enclosing iteration statement; that is, to the end of the loop body. More precisely, in each of the statements
while (/*...*/) { do { for (/*...*/) { /*...*/ /*...*/ /*...*/ continue; continue; continue; /*...*/ /*...*/ /*...*/ contin: ; contin: ; contin: ; } } while (/*...*/); }
unless the continue statement shown is in an enclosed iteration statement (in which case it is interpreted within that statement), it is equivalent to goto contin;.68
A break statement shall appear only in or as a switch body or loop body.
A break statement terminates execution of the smallest enclosing switch or iteration statement.
A return statement with an expression shall not appear in a function whose return type is void.
A return statement terminates execution of the current
function and
returns control to its caller. A function may have any number of
return statements, with and without expressions.
If a return statement with an expression is executed, the value of the expression is returned to the caller as the value of the function call expression. If the expression has a type different from that of the function in which it appears, it is converted as if it were assigned to an object of that type.
If a return statement without an expression is executed, and the value of the function call is used by the caller, the behavior is undefined. Reaching the } that terminates a function is equivalent to executing a return statement without an expression.
translation-unit: external-declaration translation-unit external-declaration
external-declaration: function-definition declaration
The storage-class specifiers auto and register shall not appear in the declaration specifiers in an external declaration.
There shall be no more than one external definition for each identifier declared with internal linkage in a translation unit. Moreover, if an identifier declared with internal linkage is used in an expression (other than as a part of the operand of a sizeof operator), there shall be exactly one external definition for the identifier in the translation unit.
As discussed in 2.1.1.1, the unit of program text after preprocessing is a translation unit, which consists of a sequence of external declarations. These are described as “external” because they appear outside any function (and hence have file scope). As discussed in 3.5, a declaration that also causes storage to be reserved for an object or a function named by the identifier is a definition.
An external definition is an external declaration that is also a definition of a function or an object. If an identifier declared with external linkage is used in an expression (other than as part of the operand of a sizeof operator), somewhere in the entire program there shall be exactly one external definition for the identifier.69
function-definition: declaration-specifiersopt declarator declaration-listopt compound-statement
The identifier declared in a function definition (which is the name of the function) shall have a function type, as specified by the declarator portion of the function definition.70
The return type of a function shall be void or an object type other than array.
The storage-class specifier, if any, in the declaration specifiers shall be either extern or static.
If the declarator includes a parameter type list, the declaration of each parameter shall include an identifier (except for the special case of a parameter list consisting of a single parameter of type void, in which there shall not be an identifier). No declaration list shall follow.
If the declarator includes an identifier list, only the identifiers it names shall be declared in the declaration list. An identifier declared as a typedef name shall not be redeclared as a parameter. The declarations in the declaration list shall contain no storage-class specifier other than register and no initializations.
The declarator in a function definition specifies the name of the
function being defined and the identifiers of its parameters. If the
declarator includes a parameter type list, the list also specifies the
types of all the parameters; such a declarator also serves as a
function prototype for later calls to the same
function in the same
translation unit. If the declarator includes an identifier list,71
the types of the parameters may be declared in a following declaration
list. Any parameter that is not declared has type int.
If a function that accepts a variable number of arguments is defined without a parameter type list that ends with the ellipsis notation, the behavior is undefined.
On entry to the function the value of each argument expression shall be converted to the type of its corresponding parameter, as if by assignment to the parameter. Array expressions and function designators as arguments are converted to pointers before the call. A declaration of a parameter as “array of type ” shall be adjusted to “pointer to type,” and a declaration of a parameter as “function returning type ” shall be adjusted to “pointer to function returning type,” as in 3.2.2.1. The resulting parameter type shall be an object type.
Each parameter has automatic storage duration. Its identifier is an lvalue.72 The layout of the storage for parameters is unspecified.
extern int max(int a, int b) { return a > b ? a : b; }
Here extern is the storage-class specifier and int is the type specifier (each of which may be omitted as those are the defaults); max(int a, int b) is the function declarator; and
{ return a > b ? a : b; }
is the function body. The following similar definition uses the identifier-list form for the parameter declarations:
extern int max(a, b) int a, b; { return a > b ? a : b; }
Here int a, b; is the declaration list for the parameters, which may be omitted because those are the defaults. The difference between these two definitions is that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls to the function, whereas the second form may not.
To pass one function to another, one might say
int f(void); /*...*/ g(f);
Note that f must be declared explicitly in the calling
function, as
its appearance in the expression g(f) was not followed by (. Then
the definition of g might read
g(int (*funcp)(void)) { /*...*/ (*funcp)() /* or funcp() ... */ }
or, equivalently,
g(int func(void)) { /*...*/ func() /* or (*func)() ... */ }
If the declaration of an identifier for an object has file scope and an initializer, the declaration is an external definition for the identifier.
A declaration of an identifier for an object that has file scope without an initializer, and without a storage-class specifier or with the storage-class specifier static, constitutes a tentative definition. If a translation unit contains one or more tentative definitions for an identifier, and the translation unit contains no external definition for that identifier, then the behavior is exactly as if the translation unit contains a file scope declaration of that identifier, with the composite type as of the end of the translation unit, with an initializer equal to 0.
If the declaration of an identifier for an object is a tentative definition and has internal linkage, the declared type shall not be an incomplete type.
int i1 = 1; /* definition, external linkage */ static int i2 = 2; /* definition, internal linkage */ extern int i3 = 3; /* definition, external linkage */ int i4; /* tentative definition, external linkage */ static int i5; /* tentative definition, internal linkage */
int i1; /* valid tentative definition, refers to previous */ int i2; /* $3.1.2.2 renders undefined, linkage disagreement */ int i3; /* valid tentative definition, refers to previous */ int i4; /* valid tentative definition, refers to previous */ int i5; /* $3.1.2.2 renders undefined, linkage disagreement */
extern int i1; /* refers to previous, whose linkage is external */ extern int i2; /* refers to previous, whose linkage is internal */ extern int i3; /* refers to previous, whose linkage is external */ extern int i4; /* refers to previous, whose linkage is external */ extern int i5; /* refers to previous, whose linkage is internal */
group: group-part group group-part
group-part: pp-tokensopt new-line if-section control-line
if-section: if-group elif-groupsopt else-groupopt endif-line
if-group: # if constant-expression new-line groupopt # ifdef identifier new-line groupopt # ifndef identifier new-line groupopt
elif-groups: elif-group elif-groups elif-group
elif-group: # elif constant-expression new-line groupopt
else-group: # else new-line groupopt
endif-line: # endif new-line
control-line: # include pp-tokens new-line # define identifier replacement-list new-line # define identifier lparen identifier-listopt ) replacement-list new-line # undef identifier new-line # line pp-tokens new-line # error pp-tokensopt new-line # pragma pp-tokensopt new-line # new-line
lparen: the left-parenthesis character without preceding white-space
replacement-list: pp-tokensopt
pp-tokens: preprocessing-token pp-tokens preprocessing-token
new-line: the new-line character
A preprocessing directive consists of a sequence of preprocessing tokens that begins with a # preprocessing token that is either the first character in the source file (optionally after white space containing no new-line characters) or that follows white space containing at least one new-line character, and is ended by the next new-line character.73
The only white-space characters that shall appear between preprocessing tokens within a preprocessing directive (from just after the introducing # preprocessing token through just before the terminating new-line character) are space and horizontal-tab (including spaces that have replaced comments in translation phase 3).
The implementation can process and skip sections of source files conditionally, include other source files, and replace macros. These capabilities are called preprocessing, because conceptually they occur before translation of the resulting translation unit.
The preprocessing tokens within a preprocessing directive are not subject to macro expansion unless otherwise stated.
The expression that controls conditional inclusion shall be an integral constant expression except that: it shall not contain a cast; identifiers (including those lexically identical to keywords) are interpreted as described below;74 and it may contain unary operator expressions of the form
defined identifier defined ( identifier )
which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is predefined or if it has been the subject of a #define preprocessing directive without an intervening #undef directive with the same subject identifier), 0 if it is not.
Each preprocessing token that remains after all macro replacements have occurred shall be in the lexical form of a token.
Preprocessing directives of the forms
# if constant-expression new-line group<opt> # elif constant-expression new-line group<opt>
check whether the controlling constant expression evaluates to nonzero.
Prior to evaluation, macro invocations in the list of preprocessing tokens that will become the controlling constant expression are replaced (except for those macro names modified by the defined unary operator), just as in normal text. If the token defined is generated as a result of this replacement process, the behavior is undefined. After all replacements are finished, the resulting preprocessing tokens are converted into tokens, and then all remaining identifiers are replaced with 0. The resulting tokens comprise the controlling constant expression which is evaluated according to the rules of 3.4 using arithmetic that has at least the ranges specified in 2.2.4.2, except that int and unsigned int act as if they have the same representation as, respectively, long and unsigned long. This includes interpreting character constants, which may involve converting escape sequences into execution character set members. Whether the numeric value for these character constants matches the value obtained when an identical character constant occurs in an expression (other than within a #if or #elif directive) is implementation-defined.75 Also, whether a single-character character constant may have a negative value is implementation-defined.
Preprocessing directives of the forms
# ifdef identifier new-line group<opt> # ifndef identifier new-line group<opt>
check whether the identifier is or is not currently defined as a macro name. Their conditions are equivalent to #if defined identifier and #if !defined identifier respectively.
Each directive's condition is checked in order. If it evaluates to false (zero), the group that it controls is skipped: directives are processed only through the name that determines the directive in order to keep track of the level of nested conditionals; the rest of the directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the group. Only the first group whose control condition evaluates to true (nonzero) is processed. If none of the conditions evaluates to true, and there is a #else directive, the group controlled by the #else is processed; lacking a #else directive, all the groups until the #endif are skipped.76
Forward references: macro replacement (3.8.3), source file inclusion (3.8.2).
A #include directive shall identify a header or source file that can be processed by the implementation.
A preprocessing directive of the form
# include < h-char-sequence > new-line
searches a sequence of implementation-defined places for a header identified uniquely by the specified sequence between the < and > delimiters, and causes the replacement of that directive by the entire contents of the header. How the places are specified or the header identified is implementation-defined.
A preprocessing directive of the form
# include " q-char-sequence " new-line
causes the replacement of that directive by the entire contents of the source file identified by the specified sequence between the delimiters. The named source file is searched for in an implementation-defined manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read
# include < h-char-sequence > new-line
with the identical contained sequence (including > characters, if any) from the original directive.
A preprocessing directive of the form
(that does not match one of the two previous forms) is permitted. The preprocessing tokens after include in the directive are processed just as in normal text. (Each identifier currently defined as a macro name is replaced by its replacement list of preprocessing tokens.) The directive resulting after all replacements shall match one of the two previous forms.77 The method by which a sequence of preprocessing tokens between a < and a > preprocessing token pair or a pair of characters is combined into a single header name preprocessing token is implementation-defined.
There shall be an implementation-defined mapping between the delimited sequence and the external source file name. The implementation shall provide unique mappings for sequences consisting of one or more letters (as defined in 2.2.1) followed by a period (.) and a single letter. The implementation may ignore the distinctions of alphabetical case and restrict the mapping to six significant characters before the period.
A #include preprocessing directive may appear in a source file that has been read because of a #include directive in another file, up to an implementation-defined nesting limit (see 2.2.4.1).
The most common uses of #include preprocessing directives are as in the following:
#include <stdio.h>
#include "myprog.h"
This example illustrates a macro-replaced #include directive:
#if VERSION == 1 #define INCFILE "vers1.h" #elif VERSION == 2 #define INCFILE "vers2.h" /* and so on */ #else #define INCFILE "versN.h" #endif /*...*/ #include INCFILE
Forward references: macro replacement (3.8.3).
Two replacement lists are identical if and only if the preprocessing tokens in both have the same number, ordering, spelling, and white-space separation, where all white-space separations are considered identical.
An identifier currently defined as a macro without use of lparen (an object-like macro) may be redefined by another #define preprocessing directive provided that the second definition is an object-like macro definition and the two replacement lists are identical.
An identifier currently defined as a macro using lparen (a function-like macro) may be redefined by another #define preprocessing directive provided that the second definition is a function-like macro definition that has the same number and spelling of parameters, and the two replacement lists are identical.
The number of arguments in an invocation of a function-like macro shall agree with the number of parameters in the macro definition, and there shall exist a ) preprocessing token that terminates the invocation.
A parameter identifier in a function-like macro shall be uniquely declared within its scope.
The identifier immediately following the define is called the macro name. Any white-space characters preceding or following the replacement list of preprocessing tokens are not considered part of the replacement list for either form of macro.
If a # preprocessing token, followed by an identifier, occurs lexically at the point at which a preprocessing directive could begin, the identifier is not subject to macro replacement.
A preprocessing directive of the form
# define identifier replacement-list new-line
defines an object-like macro that causes each subsequent instance of the macro name78 to be replaced by the replacement list of preprocessing tokens that constitute the remainder of the directive. The replacement list is then rescanned for more macro names as specified below.
A preprocessing directive of the form
# define identifier lparen identifier-listopt ) replacement-list new-line
defines a function-like macro with arguments, similar syntactically to a function call. The parameters are specified by the optional list of identifiers, whose scope extends from their declaration in the identifier list until the new-line character that terminates the #define preprocessing directive. Each subsequent instance of the function-like macro name followed by a ( as the next preprocessing token introduces the sequence of preprocessing tokens that is replaced by the replacement list in the definition (an invocation of the macro). The replaced sequence of preprocessing tokens is terminated by the matching ) preprocessing token, skipping intervening matched pairs of left and right parenthesis preprocessing tokens. Within the sequence of preprocessing tokens making up an invocation of a function-like macro, new-line is considered a normal white-space character.
The sequence of preprocessing tokens bounded by the outside-most matching parentheses forms the list of arguments for the function-like macro. The individual arguments within the list are separated by comma preprocessing tokens, but comma preprocessing tokens bounded by nested parentheses do not separate arguments. If (before argument substitution) any argument consists of no preprocessing tokens, the behavior is undefined. If there are sequences of preprocessing tokens within the list of arguments that would otherwise act as preprocessing directives, the behavior is undefined.
After the arguments for the invocation of a function-like macro have been identified, argument substitution takes place. A parameter in the replacement list, unless preceded by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is replaced by the corresponding argument after all macros contained therein have been expanded. Before being substituted, each argument's preprocessing tokens are completely macro replaced as if they formed the rest of the source file; no other preprocessing tokens are available.
Each # preprocessing token in the replacement list for a function-like macro shall be followed by a parameter as the next preprocessing token in the replacement list.
If, in the replacement list, a parameter is immediately preceded by a # preprocessing token, both are replaced by a single character string literal preprocessing token that contains the spelling of the preprocessing token sequence for the corresponding argument. Each occurrence of white space between the argument's preprocessing tokens becomes a single space character in the character string literal. White space before the first preprocessing token and after the last preprocessing token comprising the argument is deleted. Otherwise, the original spelling of each preprocessing token in the argument is retained in the character string literal, except for special handling for producing the spelling of string literals and character constants: a \ character is inserted before each and \ character of a character constant or string literal (including the delimiting characters). If the replacement that results is not a valid character string literal, the behavior is undefined. The order of evaluation of # and ## operators is unspecified.
A ## preprocessing token shall not occur at the beginning or at the end of a replacement list for either form of macro definition.
If, in the replacement list, a parameter is immediately preceded or followed by a ## preprocessing token, the parameter is replaced by the corresponding argument's preprocessing token sequence.
For both object-like and function-like macro invocations, before the replacement list is reexamined for more macro names to replace, each instance of a ## preprocessing token in the replacement list (not from an argument) is deleted and the preceding preprocessing token is concatenated with the following preprocessing token. If the result is not a valid preprocessing token, the behavior is undefined. The resulting token is available for further macro replacement. The order of evaluation of ## operators is unspecified.
After all parameters in the replacement list have been substituted, the resulting preprocessing token sequence is rescanned with the rest of the source file's preprocessing tokens for more macro names to replace.
If the name of the macro being replaced is found during this scan of the replacement list (not including the rest of the source file's preprocessing tokens), it is not replaced. Further, if any nested replacements encounter the name of the macro being replaced, it is not replaced. These nonreplaced macro name preprocessing tokens are no longer available for further replacement even if they are later (re)examined in contexts in which that macro name preprocessing token would otherwise have been replaced.
The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one.
A macro definition lasts (independent of block structure) until a corresponding #undef directive is encountered or (if none is encountered) until the end of the translation unit.
A preprocessing directive of the form
# undef identifier new-line
causes the specified identifier no longer to be defined as a macro name. It is ignored if the specified identifier is not currently defined as a macro name.
The simplest use of this facility is to define a “manifest constant,” as in
#define TABSIZE 100
int table[TABSIZE];
The following defines a function-like macro whose value is the maximum of its arguments. It has the advantages of working for any compatible types of the arguments and of generating in-line code without the overhead of function calling. It has the disadvantages of evaluating one or the other of its arguments a second time (including side effects) and of generating more code than a function if invoked several times.
#define max(a, b) ((a) > (b) ? (a) : (b))
The parentheses ensure that the arguments and the resulting expression are bound properly.
To illustrate the rules for redefinition and reexamination, the sequence
#define x 3 #define f(a) f(x * (a)) #undef x #define x 2 #define g f #define z z[0] #define h g(~ #define m(a) a(w) #define w 0,1 #define t(a) a
f(y+1) + f(f(z)) % t(t(g)(0) + t)(1); g(x+(3,4)-w) | h 5) & m (f)^m(m);
results in
f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1); f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
To illustrate the rules for creating character string literals and concatenating tokens, the sequence
#define str(s) # s #define xstr(s) str(s) #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \ x ## s, x ## t) #define INCFILE(n) vers ## n /* from previous #include example */ #define glue(a, b) a ## b #define xglue(a, b) glue(a, b) #define HIGHLOW "hello" #define LOW LOW ", world"
debug(1, 2); fputs(str(strncmp("abc\0d", "abc", '\4') /* this goes away */ == 0) str(: @\n), s); #include xstr(INCFILE(2).h) glue(HIGH, LOW); xglue(HIGH, LOW)
results in
printf("x" "1" "= %d, x" "2" "= %s", x1, x2); fputs("strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n", s); #include "vers2.h" (after macro replacement, before file access) "hello"; "hello" ", world"
or, after concatenation of the character string literals,
printf("x1= %d, x2= %s", x1, x2); fputs("strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n", s); #include "vers2.h" (after macro replacement, before file access) "hello"; "hello, world"
Space around the # and ## tokens in the macro definition is optional.
And finally, to demonstrate the redefinition rules, the following sequence is valid.
#define OBJ_LIKE (1-1) #define OBJ_LIKE /* white space */ (1-1) /* other */ #define FTN_LIKE(a) ( a ) #define FTN_LIKE( a )( /* note the white space */ \ a /* other stuff on this line */ )
But the following redefinitions are invalid:
#define OBJ_LIKE (0) /* different token sequence */ #define OBJ_LIKE (1 - 1) /* different white space */ #define FTN_LIKE(b) ( a ) /* different parameter usage */ #define FTN_LIKE(b) ( b ) /* different parameter spelling */
The string literal of a #line directive, if present, shall be a character string literal.
The line number of the current source line is one greater than the number of new-line characters read or introduced in translation phase 1 (2.1.1.2) while processing the source file to the current token.
A preprocessing directive of the form
# line digit-sequence new-line
causes the implementation to behave as if the following sequence of source lines begins with a source line that has a line number as specified by the digit sequence (interpreted as a decimal integer).
A preprocessing directive of the form
# line digit-sequence " s-char-sequenceopt " new-line
sets the line number similarly and changes the presumed name of the source file to be the contents of the character string literal.
A preprocessing directive of the form
(that does not match one of the two previous forms) is permitted. The preprocessing tokens after line on the directive are processed just as in normal text (each identifier currently defined as a macro name is replaced by its replacement list of preprocessing tokens). The directive resulting after all replacements shall match one of the two previous forms and is then processed as appropriate.
A preprocessing directive of the form
causes the implementation to produce a diagnostic message that includes the specified sequence of preprocessing tokens.
A preprocessing directive of the form
# pragma pp-tokensopt new-line
causes the implementation to behave in an implementation-defined manner. Any pragma that is not recognized by the implementation is ignored.
The following
macro names shall be defined by the implementation:
The line number of the current source line (a decimal constant). The
presumed name of the source file (a character string literal). The
date of translation of the source file (a character string literal of
the form Mmm dd yyyy, where the names of the months are the same as
those generated by the asctime
function, and the first character of dd
is a space character if the value is less than 10). If the date of
translation is not available, an implementation-defined valid date
shall be supplied. The time of translation of the source file (a
character string literal of the form hh:mm:ss as in the time generated
by the asctime
function). If the time of translation is not
available, an implementation-defined valid time shall be supplied.
the decimal constant 1.79
The values of the predefined
macros (except for __LINE__ and
__FILE__ ) remain constant throughout the translation unit.
None of these macro names, nor the identifier defined, shall be the subject of a #define or a #undef preprocessing directive. All predefined macro names shall begin with a leading underscore followed by an upper-case letter or a second underscore.
Forward references: the asctime
function (4.12.3.1).
Restriction of the significance of an external name to fewer than 31 characters or to only one case is an obsolescent feature that is a concession to existing implementations.
Lower-case letters as escape sequences are reserved for future standardization. Other characters may be used in extensions.
The placement of a storage-class specifier other than at the beginning of the declaration specifiers in a declaration is an obsolescent feature.
The use of function declarators with empty parentheses (not prototype-format parameter type declarators) is an obsolescent feature.
The use of function definitions with separate parameter identifier and declaration lists (not prototype-format parameter type and identifier declarators) is an obsolescent feature.
A string is a contiguous sequence of characters terminated by and including the first null character. It is represented by a pointer to its initial (lowest addressed) character and its length is the number of characters preceding the null character.
A letter is a printing character in the execution character set corresponding to any of the 52 required lower-case and upper-case letters in the source character set, listed in 2.2.1.
The decimal-point character is the character used by functions that
convert floating-point numbers to or from character sequences to
denote the beginning of the fractional part of such character
sequences.80 It is represented in the text and examples by a period,
but may be changed by the setlocale
function.
Forward references: character handling (4.3), the setlocale
function
(4.4.1.1).
Each library function is declared in a header,81 whose contents are made available by the #include preprocessing directive. The header declares a set of related functions, plus any necessary types and additional macros needed to facilitate their use. Each header declares and defines only those identifiers listed in its associated section. All external identifiers declared in any of the headers are reserved, whether or not the associated header is included. All external identifiers that begin with an underscore are reserved. All other identifiers that begin with an underscore and either an upper-case letter or another underscore are reserved. If the program defines an external identifier with the same name as a reserved external identifier, even in a semantically equivalent form, the behavior is undefined.82
The standard headers are
<assert.h>
<locale.h>
<stddef.h>
<ctype.h>
<math.h>
<stdio.h>
<errno.h>
<setjmp.h>
<stdlib.h>
<float.h>
<signal.h>
<string.h>
<limits.h>
<stdarg.h>
<time.h>
If a file with the same name as one of the above < and > delimited sequences, not provided as part of the implementation, is placed in any of the standard places for a source file to be included, the behavior is undefined.
Headers may be included in any order; each may be included more
than once in a given scope, with no effect different from being
included only once, except that the effect of including <assert.h>
depends on the definition of NDEBUG. If used, a header shall be
included outside of any external declaration or definition, and it
shall first be included before the first reference to any of the
functions or objects it declares, or to any of the types or macros it
defines. Furthermore, the program shall not have any macros with
names lexically identical to keywords currently defined prior to the
inclusion.
Forward references: diagnostics (4.2).
<errno.h>
The header <errno.h>
defines several macros, all relating to the
reporting of error conditions.
The macros are
EDOM ERANGE
which expand to distinct nonzero integral constant expressions; and
errno
which expands to a modifiable lvalue83 that has type int, the value of which is set to a positive error number by several library functions. It is unspecified whether errno is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual object, or a program defines an external identifier with the name errno, the behavior is undefined.
The value of errno is zero at program startup, but is never set to zero by any library function.84 The value of errno may be set to nonzero by a library function call whether or not there is an error, provided the use of errno is not documented in the description of the function in the Standard.
Additional macro definitions, beginning with E and a digit or E and an upper-case letter,85 may also be specified by the implementation.
<float.h>
and <limits.h>
The headers <float.h>
and <limits.h>
define several macros that
expand to various limits and parameters.
The macros, their meanings, and their minimum magnitudes are listed in 2.2.4.2.
<stddef.h>
The following types and macros are defined in the standard header
<stddef.h>
. Some are also defined in other headers, as noted in
their respective sections.
The types are
ptrdiff_t
which is the signed integral type of the result of subtracting two pointers;
size_t
which is the unsigned integral type of the result of the sizeof operator; and
wchar_t
which is an integral type whose range of values can represent distinct codes for all members of the largest extended character set specified among the supported locales; the null character shall have the code value zero and each member of the basic character set defined in 2.2.1 shall have a code value equal to its value when used as the lone character in an integer character constant.
The macros are
NULL
which expands to an implementation-defined null pointer constant; and
offsetof( type, member-designator)
which expands to an integral constant expression that has type size_t, the value of which is the offset in bytes, to the structure member (designated by member-designator ), from the beginning of its structure (designated by type ). The member-designator shall be such that given
static type t;
then the expression &(t. member-designator ) evaluates to an address constant. (If the specified member is a bit-field, the behavior is undefined.)
Forward references: localization (4.4).
Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow. If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer), the behavior is undefined. Any function declared in a header may be implemented as a macro defined in the header, so a library function should not be declared explicitly if its header is included. Any macro definition of a function can be suppressed locally by enclosing the name of the function in parentheses, because the name is then not followed by the left parenthesis that indicates expansion of a macro function name. For the same syntactic reason, it is permitted to take the address of a library function even if it is also defined as a macro.86 The use of #undef to remove any macro definition will also ensure that an actual function is referred to. Any invocation of a library function that is implemented as a macro will expand to code that evaluates each of its arguments exactly once, fully protected by parentheses where necessary, so it is generally safe to use arbitrary expressions as arguments. Likewise, those function-like macros described in the following sections may be invoked in an expression anywhere a function with a compatible return type could be called.87
Provided that a library function can be declared without reference to any type defined in a header, it is also permissible to declare the function, either explicitly or implicitly, and use it without including its associated header. If a function that accepts a variable number of arguments is not declared (explicitly or by including its associated header), the behavior is undefined.
The function atoi may be used in any of several ways:
#include <stdlib.h>
const char *str;
/*...*/
i = atoi(str);
#include <stdlib.h>
#undef atoi
const char *str;
/*...*/
i = atoi(str);
or
#include <stdlib.h>
const char *str;
/*...*/
i = (atoi)(str);
extern int atoi(const char *); const char *str; /*...*/ i = atoi(str);
const char *str; /*...*/ i = atoi(str);
<assert.h>
The header <assert.h>
defines the assert
macro and refers to
another macro,
NDEBUG
which is not defined by <assert.h>
. If NDEBUG is defined as a macro
name at the point in the source file where <assert.h>
is included, the
assert macro is defined simply as
#define assert(ignore) ((void)0)
The assert
macro shall be implemented as a macro, not as an actual
function. If the macro definition is suppressed in order to access an
actual function, the behavior is undefined.
assert
macro #include <assert.h>
void assert(int expression);
The assert
macro puts diagnostics into programs. When it is
executed, if expression is false (that is, compares equal to 0), the
assert macro writes information about the particular call that failed
(including the text of the argument, the name of the source file, and
the source line number EM the latter are respectively the values of
the preprocessing
macros __FILE__ and __LINE__ ) on the standard error
file in an implementation-defined format.88
expression, xyz, nnn It then calls the abort
function.
The assert
macro returns no value.
Forward references: the abort
function (4.10.4.1).
<ctype.h>
The header <ctype.h>
declares several functions useful for testing
and mapping characters.89 In all cases the argument is an int, the
value of which shall be representable as an unsigned char or shall
equal the value of the macro EOF. If the argument has any other
value, the behavior is undefined.
The behavior of these functions is affected by the current locale. Those functions that have no implementation-defined aspects in the C locale are noted below.
The term printing character refers to a member of an implementation-defined set of characters, each of which occupies one printing position on a display device; the term control character refers to a member of an implementation-defined set of characters that are not printing characters.90
Forward references: EOF (4.9.1), localization (4.4).
The functions in this section return nonzero (true) if and only if the value of the argument c conforms to that in the description of the function.
isalnum
function #include <ctype.h>
int isalnum(int c);
The isalnum
function tests for any character for which isalpha or
isdigit is true.
isalpha
function #include <ctype.h>
int isalpha(int c);
The isalpha
function tests for any character for which isupper or
islower is true, or any of an implementation-defined set of characters
for which none of iscntrl, isdigit, ispunct, or isspace is true.
In the C locale, isalpha returns true only for the characters for
which isupper or islower is true.
iscntrl
function #include <ctype.h>
int iscntrl(int c);
The iscntrl
function tests for any control character.
isdigit
function #include <ctype.h>
int isdigit(int c);
The isdigit
function tests for any decimal-digit character (as
defined in 2.2.1).
isgraph
function #include <ctype.h>
int isgraph(int c);
The isgraph
function tests for any printing character except space (' ').
islower
function #include <ctype.h>
int islower(int c);
The islower
function tests for any lower-case letter or any of an
implementation-defined set of characters for which none of iscntrl,
isdigit, ispunct, or isspace is true. In the C locale, islower
returns true only for the characters defined as lower-case letters (as
defined in 2.2.1).
isprint
function #include <ctype.h>
int isprint(int c);
The isprint
function tests for any printing character including
space (' ').
ispunct
function #include <ctype.h>
int ispunct(int c);
The ispunct
function tests for any printing character except space
(' ') or a character for which isalnum is true.
isspace
function #include <ctype.h>
int isspace(int c);
The isspace
function tests for the standard white-space characters
or for any of an implementation-defined set of characters for which
isalnum is false. The standard white-space characters are the
following: space (' '), form feed ('\f'), new-line ('\n'), carriage
return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
C locale, isspace returns true only for the standard white-space
characters.
isupper
function #include <ctype.h>
int isupper(int c);
The isupper
function tests for any upper-case letter or any of an
implementation-defined set of characters for which none of iscntrl,
isdigit, ispunct, or isspace is true. In the C locale, isupper
returns true only for the characters defined as upper-case letters (as
defined in 2.2.1).
isxdigit
function #include <ctype.h>
int isxdigit(int c);
The isxdigit
function tests for any hexadecimal-digit character (as
defined in 3.1.3.2).
tolower
function #include <ctype.h>
int tolower(int c);
The tolower
function converts an upper-case letter to the
corresponding lower-case letter.
If the argument is an upper-case letter, the tolower
function
returns the corresponding lower-case letter if there is one; otherwise
the argument is returned unchanged. In the C locale, tolower maps
only the characters for which isupper is true to the corresponding
characters for which islower is true.
toupper
function #include <ctype.h>
int toupper(int c);
The toupper
function converts a lower-case letter to the corresponding upper-case letter.
If the argument is a lower-case letter, the toupper
function
returns the corresponding upper-case letter if there is one; otherwise
the argument is returned unchanged. In the C locale, toupper maps
only the characters for which islower is true to the corresponding
characters for which isupper is true.
<locale.h>
The header <locale.h>
declares two functions, one type, and defines
several macros.
The type is
struct lconv
which contains members related to the formatting of numeric values. The structure shall contain at least the following members, in any order. The semantics of the members and their normal ranges is explained in 4.4.2.1. In the C locale, the members shall have the values specified in the comments.
char *decimal_point; /* "." */ char *thousands_sep; /* "" */ char *grouping; /* "" */ char *int_curr_symbol; /* "" */ char *currency_symbol; /* "" */ char *mon_decimal_point; /* "" */ char *mon_thousands_sep; /* "" */ char *mon_grouping; /* "" */ char *positive_sign; /* "" */ char *negative_sign; /* "" */ char int_frac_digits; /* CHAR_MAX */ char frac_digits; /* CHAR_MAX */ char p_cs_precedes; /* CHAR_MAX */ char p_sep_by_space; /* CHAR_MAX */ char n_cs_precedes; /* CHAR_MAX */ char n_sep_by_space; /* CHAR_MAX */ char p_sign_posn; /* CHAR_MAX */ char n_sign_posn; /* CHAR_MAX */
The macros defined are NULL (described in 4.1.5); and
LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME
which expand to distinct integral constant expressions, suitable for
use as the first argument to the setlocale
function. Additional macro
definitions, beginning with the characters LC_ and an upper-case
letter,91 may also be specified by the implementation.
setlocale
function #include <locale.h>
char *setlocale(int category, const char *locale);
The setlocale
function selects the appropriate portion of the
program's locale as specified by the category and locale arguments.
The setlocale
function may be used to change or query the program's
entire current locale or portions thereof. The value LC_ALL for
category names the program's entire locale; the other values for
category name only a portion of the program's locale. LC_COLLATE
affects the behavior of the strcoll and strxfrm functions. LC_CTYPE
affects the behavior of the character handling functions92 and the
multibyte functions. LC_MONETARY affects the monetary formatting
information returned by the localeconv
function. LC_NUMERIC affects
the decimal-point character for the formatted input/output functions
and the string conversion functions, as well as the non-monetary
formatting information returned by the localeconv
function. LC_TIME
affects the behavior of the strftime
function.
A value of "C" for locale specifies the minimal environment for C translation; a value of "" for locale specifies the implementation-defined native environment. Other implementation-defined strings may be passed as the second argument to setlocale.
At program startup, the equivalent of
setlocale(LC_ALL, "C");
is executed.
The implementation shall behave as if no library function calls the setlocale function.
If a pointer to a string is given for locale and the selection can
be honored, the setlocale
function returns the string associated with
the specified category for the new locale. If the selection cannot be
honored, the setlocale
function returns a null pointer and the
program's locale is not changed.
A null pointer for locale causes the setlocale
function to return
the string associated with the category for the program's current
locale; the program's locale is not changed.
The string returned by the setlocale
function is such that a
subsequent call with that string and its associated category will
restore that part of the program's locale. The string returned shall
not be modified by the program, but may be overwritten by a subsequent
call to the setlocale
function.
Forward references: formatted input/output functions (4.9.6), the
multibyte character functions (4.10.7), the multibyte string
functions (4.10.8), string conversion functions (4.10.1), the
strcoll function (4.11.4.3), the strftime
function (4.12.3.5), the
strxfrm function (4.11.4.5).
localeconv
function #include <locale.h>
struct lconv *localeconv(void);
The localeconv
function sets the components of an object with type
struct lconv with values appropriate for the formatting of numeric
quantities (monetary and otherwise) according to the rules of the
current locale.
The members of the structure with type char * are strings, any of which (except decimal_point ) can point to, to indicate that the value is not available in the current locale or is of zero length. The members with type char are nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not available in the current locale. The members include the following: The decimal-point character used to format non-monetary quantities. The character used to separate groups of digits to the left of the decimal-point character in formatted non-monetary quantities. A string whose elements indicate the size of each group of digits in formatted non-monetary quantities. The international currency symbol applicable to the current locale. The first three characters contain the alphabetic international currency symbol in accordance with those specified in ISO 4217 Codes for the Representation of Currency and Funds.The fourth character (immediately preceding the null character) is the character used to separate the international currency symbol from the monetary quantity. The local currency symbol applicable to the current locale. The decimal-point used to format monetary quantities. The separator for groups of digits to the left of the decimal-point in formatted monetary quantities. A string whose elements indicate the size of each group of digits in formatted monetary quantities. The string used to indicate a nonnegative-valued formatted monetary quantity. The string used to indicate a negative-valued formatted monetary quantity. The number of fractional digits (those to the right of the decimal-point) to be displayed in a internationally formatted monetary quantity. The number of fractional digits (those to the right of the decimal-point) to be displayed in a formatted monetary quantity. Set to 1 or 0 if the currency_symbol respectively precedes or succeeds the value for a nonnegative formatted monetary quantity. Set to 1 or 0 if the currency_symbol respectively is or is not separated by a space from the value for a nonnegative formatted monetary quantity. Set to 1 or 0 if the currency_symbol respectively precedes or succeeds the value for a negative formatted monetary quantity. Set to 1 or 0 if the currency_symbol respectively is or is not separated by a space from the value for a negative formatted monetary quantity. Set to a value indicating the positioning of the positive_sign for a nonnegative formatted monetary quantity. Set to a value indicating the positioning of the negative_sign for a negative formatted monetary quantity.
The elements of grouping and mon_grouping are interpreted according to the following: No further grouping is to be performed. The previous element is to be repeatedly used for the remainder of the digits. The value is the number of digits that comprise the current group. The next element is examined to determine the size of the next group of digits to the left of the current group.
The value of p_sign_posn and n_sign_posn is interpreted according to the following: Parentheses surround the quantity and currency_symbol. The sign string precedes the quantity and currency_symbol. The sign string succeeds the quantity and currency_symbol. The sign string immediately precedes the currency_symbol. The sign string immediately succeeds the currency_symbol.
The implementation shall behave as if no library function calls the localeconv function.
The localeconv
function returns a pointer to the filled-in object.
The structure pointed to by the return value shall not be modified by
the program, but may be overwritten by a subsequent call to the
localeconv function. In addition, calls to the setlocale
function
with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may overwrite the
contents of the structure.
The following table illustrates the rules used by four countries to format monetary quantities.
Country Positive format Negative format International format
Italy L.1.234 -L.1.234 ITL.1.234 Netherlands F 1.234,56 F -1.234,56 NLG 1.234,56 Norway kr1.234,56 kr1.234,56- NOK 1.234,56 Switzerland SFrs.1,234.56 SFrs.1,234.56C CHF 1,234.56
For these four countries, the respective values for the monetary members of the structure returned by localeconv are:
Italy Netherlands Norway Switzerland
int_curr_symbol "ITL." "NLG " "NOK " "CHF " currency_symbol "L." "F" "kr" "SFrs." mon_decimal_point "" "," "," "." mon_thousands_sep "." "." "." "," mon_grouping "\3" "\3" "\3" "\3" positive_sign "" "" "" "" negative_sign "-" "-" "-" "C" int_frac_digits 0 2 2 2 frac_digits 0 2 2 2 p_cs_precedes 1 1 1 1 p_sep_by_space 0 1 0 0 n_cs_precedes 1 1 1 1 n_sep_by_space 0 1 0 0 p_sign_posn 1 1 1 1 n_sign_posn 1 4 2 2
<math.h>
The header <math.h>
declares several mathematical functions and
defines one macro. The functions take double-precision arguments and
return double-precision values.93 Integer arithmetic functions and
conversion functions are discussed later.
The macro defined is
HUGE_VAL
which expands to a positive double expression, not necessarily representable as a float.
Forward references: integer arithmetic functions (4.10.6), the atof
function (4.10.1.1), the strtod
function (4.10.1.4).
The behavior of each of these functions is defined for all representable values of its input arguments. Each function shall execute as if it were a single operation, without generating any externally visible exceptions.
For all functions, a domain error occurs if an input argument is
outside the domain over which the mathematical
function is defined.
The description of each function lists any required domain errors; an
implementation may define additional domain errors, provided that such
errors are consistent with the mathematical definition of the
function.94 On a domain error, the function returns an
implementation-defined value; the value of the macro EDOM is stored in
errno.
Similarly, a range error occurs if the result of the function cannot be represented as a double value. If the result overflows (the magnitude of the result is so large that it cannot be represented in an object of the specified type), the function returns the value of the macro HUGE_VAL, with the same sign as the correct value of the function; the value of the macro ERANGE is stored in errno. If the result underflows (the magnitude of the result is so small that it cannot be represented in an object of the specified type), the function returns zero; whether the integer expression errno acquires the value of the macro ERANGE is implementation-defined.
acos
function #include <math.h>
double acos(double x);
The acos
function computes the principal value of the arc cosine of x.
A domain error occurs for arguments not in the range [-1, +1].
The acos
function returns the arc cosine in the range [0, PI] radians.
asin
function #include <math.h>
double asin(double x);
The asin
function computes the principal value of the arc sine of x.
A domain error occurs for arguments not in the range [-1, +1].
The asin
function returns the arc sine in the range [-PI/2, +PI/2]
radians.
atan
function #include <math.h>
double atan(double x);
The atan
function computes the principal value of the arc tangent of x.
The atan
function returns the arc tangent in the range [-PI/2, +PI/2]
radians.
atan2
function #include <math.h>
double atan2(double y, double x);
The atan2
function computes the principal value of the arc tangent
of y/x, using the signs of both arguments to determine the quadrant
of the return value. A domain error may occur if both arguments are
zero.
The atan2
function returns the arc tangent of y/x, in the range
[-PI, +PI] radians.
cos
function #include <math.h>
double cos(double x);
The cos
function computes the cosine of x (measured in radians). A
large magnitude argument may yield a result with little or no
significance.
The cos
function returns the cosine value.
sin
function #include <math.h>
double sin(double x);
The sin
function computes the sine of x (measured in radians). A
large magnitude argument may yield a result with little or no
significance.
The sin
function returns the sine value.
tan
function #include <math.h>
double tan(double x);
The tan
function returns the tangent of x (measured in radians). A
large magnitude argument may yield a result with little or no significance.
The tan
function returns the tangent value.
cosh
function #include <math.h>
double cosh(double x);
The cosh
function computes the hyperbolic cosine of x. A range
error occurs if the magnitude of x is too large.
The cosh
function returns the hyperbolic cosine value.
sinh
function #include <math.h>
double sinh(double x);
The sinh
function computes the hyperbolic sine of x. A
range error occurs if the magnitude of x is too large.
The sinh
function returns the hyperbolic sine value.
tanh
function #include <math.h>
double tanh(double x);
The tanh
function computes the hyperbolic tangent of x.
The tanh
function returns the hyperbolic tangent value.
exp
function #include <math.h>
double exp(double x);
The exp
function computes the exponential
function of x. A range
error occurs if the magnitude of x is too large.
The exp
function returns the exponential value.
frexp
function #include <math.h>
double frexp(double value, int *exp);
The frexp
function breaks a floating-point number into a normalized
fraction and an integral power of 2. It stores the integer in the int
object pointed to by exp.
The frexp
function returns the value x, such that x is a double
with magnitude in the interval [1/2, 1) or zero, and value equals x
times 2 raised to the power *exp. If value is zero, both parts of
the result are zero.
ldexp
function #include <math.h>
double ldexp(double x, int exp);
The ldexp
function multiplies a floating-point number by an
integral power of 2. A range error may occur.
The ldexp
function returns the value of x times 2 raised to the
power exp.
log
function #include <math.h>
double log(double x);
The log
function computes the natural logarithm of x. A domain
error occurs if the argument is negative. A range error occurs if the
argument is zero and the logarithm of zero cannot be represented.
The log
function returns the natural logarithm.
log10
function #include <math.h>
double log10(double x);
The log10
function computes the base-ten logarithm of x. A domain
error occurs if the argument is negative. A range error occurs if the
argument is zero and the logarithm of zero cannot be represented.
The log10
function returns the base-ten logarithm.
modf
function #include <math.h>
double modf(double value, double *iptr);
The modf
function breaks the argument value into integral and
fractional parts, each of which has the same sign as the argument. It
stores the integral part as a double in the object pointed to by iptr.
The modf
function returns the signed fractional part of value.
pow
function #include <math.h>
double pow(double x, double y);
The pow
function computes x raised to the power y. A domain error
occurs if x is negative and y is not an integer. A domain error
occurs if the result cannot be represented when x is zero and y is
less than or equal to zero. A range error may occur.
The pow
function returns the value of x raised to the power y.
sqrt
function #include <math.h>
double sqrt(double x);
The sqrt
function computes the nonnegative square root of x. A
domain error occurs if the argument is negative.
The sqrt
function returns the value of the square root.
ceil
function #include <math.h>
double ceil(double x);
The ceil
function computes the smallest integral value not less than x.
The ceil
function returns the smallest integral value not less than
x, expressed as a double.
fabs
function #include <math.h>
double fabs(double x);
The fabs
function computes the absolute value of a floating-point
number x.
The fabs
function returns the absolute value of x.
floor
function #include <math.h>
double floor(double x);
The floor
function computes the largest integral value not greater
than x.
The floor
function returns the largest integral value not greater
than x, expressed as a double.
fmod
function #include <math.h>
double fmod(double x, double y);
The fmod
function computes the floating-point remainder of x/y.
The fmod
function returns the value x i y, for some integer i such
that, if y is nonzero, the result has the same sign as x and magnitude
less than the magnitude of y. If y is zero, whether a domain error
occurs or the fmod
function returns zero is implementation-defined.
<setjmp.h>
The header <setjmp.h>
defines the macro setjmp, and declares one
function and one type, for bypassing the normal
function call and
return discipline.95
The type declared is
jmp_buf
which is an array type suitable for holding the information needed to restore a calling environment.
It is unspecified whether setjmp is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual function, or a program defines an external identifier with the name setjmp, the behavior is undefined.
setjmp
macro #include <setjmp.h>
int setjmp(jmp_buf env);
The setjmp
macro saves its calling environment in its jmp_buf
argument for later use by the longjmp
function.
If the return is from a direct invocation, the setjmp
macro returns
the value zero. If the return is from a call to the longjmp
function,
the setjmp
macro returns a nonzero value.
An invocation of the setjmp
macro shall appear only in one of the
following contexts:
longjmp
function #include <setjmp.h>
void longjmp(jmp_buf env, int val);
The longjmp
function restores the environment saved by the most
recent invocation of the setjmp
macro in the same invocation of the
program, with the corresponding jmp_buf argument. If there has been
no such invocation, or if the function containing the invocation of
the setjmp
macro has terminated execution96 in the interim, the
behavior is undefined.
All accessible objects have values as of the time longjmp was called, except that the values of objects of automatic storage duration that do not have volatile type and have been changed between the setjmp invocation and longjmp call are indeterminate.
As it bypasses the usual
function call and return mechanisms, the
longjmp function shall execute correctly in contexts of interrupts,
signals and any of their associated functions. However, if the
longjmp function is invoked from a nested signal handler (that is,
from a function invoked as a result of a signal raised during the
handling of another signal), the behavior is undefined.
After longjmp is completed, program execution continues as if the
corresponding invocation of the setjmp
macro had just returned the
value specified by val. The longjmp
function cannot cause the setjmp
macro to return the value 0; if val is 0, the setjmp
macro returns the
value 1.
<signal.h>
The header <signal.h>
declares a type and two functions and defines
several macros, for handling various signals (conditions that may be
reported during program execution).
The type defined is
sig_atomic_t
which is the integral type of an object that can be accessed as an atomic entity, even in the presence of asynchronous interrupts.
The macros defined are
SIG_DFL SIG_ERR SIG_IGN
which expand to distinct constant expressions that have type compatible with the second argument to and the return value of the signal function, and whose value compares unequal to the address of any declarable function; and the following, each of which expands to a positive integral constant expression that is the signal number corresponding to the specified condition:
SIGABRT abnormal termination, such as is initiated by the abort
function
SIGFPE an erroneous arithmetic operation, such as zero divide or an operation resulting in overflow
SIGILL detection of an invalid function image, such as an illegal instruction
SIGINT receipt of an interactive attention signal
SIGSEGV an invalid access to storage
SIGTERM a termination request sent to the program
An implementation need not generate any of these signals, except as
a result of explicit calls to the raise
function. Additional signals
and pointers to undeclarable functions, with macro definitions
beginning, respectively, with the letters SIG and an upper-case letter
or with SIG_ and an upper-case letter,97 may also be specified by
the implementation. The complete set of signals, their semantics, and
their default handling is implementation-defined; all signal values
shall be positive.
signal
function #include <signal.h>
void (*signal(int sig, void (*func)(int)))(int);
The signal
function chooses one of three ways in which receipt of
the signal number sig is to be subsequently handled. If the value of
func is SIG_DFL, default handling for that signal will occur. If the
value of func is SIG_IGN, the signal will be ignored. Otherwise,
func shall point to a function to be called when that signal occurs.
Such a function is called a signal handler.
When a signal occurs, if func points to a function, first the equivalent of signal(sig, SIG_DFL); is executed or an implementation-defined blocking of the signal is performed. (If the value of sig is SIGILL, whether the reset to SIG_DFL occurs is implementation-defined.) Next the equivalent of (*func)(sig); is executed. The function func may terminate by executing a return statement or by calling the abort, exit, or longjmp function. If func executes a return statement and the value of sig was SIGFPE or any other implementation-defined value corresponding to a computational exception, the behavior is undefined. Otherwise, the program will resume execution at the point it was interrupted.
If the signal occurs other than as the result of calling the abort or raise function, the behavior is undefined if the signal handler calls any function in the standard library other than the signal function itself or refers to any object with static storage duration other than by assigning a value to a static storage duration variable of type volatile sig_atomic_t. Furthermore, if such a call to the signal function results in a SIG_ERR return, the value of errno is indeterminate.
At program startup, the equivalent of
signal(sig, SIG_IGN);
may be executed for some signals selected in an implementation-defined manner; the equivalent of
signal(sig, SIG_DFL);
is executed for all other signals defined by the implementation.
The implementation shall behave as if no library function calls the signal function.
If the request can be honored, the signal
function returns the
value of func for the most recent call to signal for the specified
signal sig. Otherwise, a value of SIG_ERR is returned and a positive
value is stored in errno.
Forward references: the abort
function (4.10.4.1).
<stdarg.h>
The header <stdarg.h>
declares a type and defines three macros, for
advancing through a list of arguments whose number and types are not
known to the called
function when it is translated.
A function may be called with a variable number of arguments of varying types. As described in 3.7.1, its parameter list contains one or more parameters. The rightmost parameter plays a special role in the access mechanism, and will be designated parmN in this description.
The type declared is
va_list
which is a type suitable for holding information needed by the macros
va_start, va_arg, and va_end. If access to the varying arguments
is desired, the called
function shall declare an object (referred to
as ap in this section) having type va_list. The object ap may be
passed as an argument to another function; if that function invokes
the va_arg
macro with parameter ap, the value of ap in the calling
function is indeterminate and shall be passed to the va_end
macro
prior to any further reference to ap.
The va_start and va_arg macros described in this section shall be implemented as macros, not as actual functions. It is unspecified whether va_end is a macro or an identifier declared with external linkage. If a macro definition is suppressed in order to access an actual function, or a program defines an external identifier with the name va_end, the behavior is undefined. The va_start and va_end macros shall be invoked in the function accepting a varying number of arguments, if access to the varying arguments is desired.
va_start
macro #include <stdarg.h>
void va_start(va_list ap, parmN);
The va_start
macro shall be invoked before any access to the
unnamed arguments.
The va_start
macro initializes ap for subsequent use by va_arg and
va_end.
The parameter parmN is the identifier of the rightmost parameter in the variable parameter list in the function definition (the one just before the,... ). If the parameter parmN is declared with the register storage class, with a function or array type, or with a type that is not compatible with the type that results after application of the default argument promotions, the behavior is undefined.
The va_start
macro returns no value.
va_arg
macro #include <stdarg.h>
type va_arg(va_list ap, type);
The va_arg
macro expands to an expression that has the type and
value of the next argument in the call. The parameter ap shall be the
same as the va_list ap initialized by va_start. Each invocation of
va_arg modifies ap so that the values of successive arguments are
returned in turn. The parameter type is a type name specified such
that the type of a pointer to an object that has the specified type
can be obtained simply by postfixing a * to type. If there is no
actual next argument, or if type is not compatible with the type of
the actual next argument (as promoted according to the default
argument promotions), the behavior is undefined.
The first invocation of the va_arg
macro after that of the va_start
macro returns the value of the argument after that specified by parmN.
Successive invocations return the values of the remaining arguments
in succession.
va_end
macro #include <stdarg.h>
void va_end(va_list ap);
The va_end
macro facilitates a normal return from the function
whose variable argument list was referred to by the expansion of
va_start that initialized the va_list ap. The va_end
macro may
modify ap so that it is no longer usable (without an intervening
invocation of va_start ). If there is no corresponding invocation of
the va_start
macro, or if the va_end
macro is not invoked before the
return, the behavior is undefined.
The va_end
macro returns no value.
The function f1 gathers into an array a list of arguments that are pointers to strings (but not more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of pointers is specified by the first argument to f1.
#include <stdarg.h>
#define MAXARGS 31
void f1(int n_ptrs, ...) { va_list ap; char *array[MAXARGS]; int ptr_no = 0;
if (n_ptrs > MAXARGS) n_ptrs = MAXARGS; va_start(ap, n_ptrs); while (ptr_no < n_ptrs) array[ptr_no++] = va_arg(ap, char *); va_end(ap); f2(n_ptrs, array); }
Each call to f1 shall have visible the definition of the function or a declaration such as
void f1(int, ...);
<stdio.h>
The header <stdio.h>
declares three types, several macros, and many
functions for performing input and output.
The types declared are size_t (described in 4.1.5);
FILE
which is an object type capable of recording all the information needed to control a stream, including its file position indicator, a pointer to its associated buffer, an error indicator that records whether a read/write error has occurred, and an end-of-file indicator that records whether the end of the file has been reached; and
fpos_t
which is an object type capable of recording all the information needed to specify uniquely every position within a file.
The macros are NULL (described in 4.1.5);
_IOFBF _IOLBF _IONBF
which expand to distinct integral constant expressions, suitable for
use as the third argument to the setvbuf
function;
BUFSIZ
which expands to an integral constant expression, which is the size of
the buffer used by the setbuf
function;
EOF
which expands to a negative integral constant expression that is returned by several functions to indicate end-of-file,that is, no more input from a stream;
FOPEN_MAX
which expands to an integral constant expression that is the minimum number of files that the implementation guarantees can be open simultaneously;
FILENAME_MAX
which expands to an integral constant expression that is the maximum length for a file name string that the implementation guarantees can be opened;98
L_tmpnam
which expands to an integral constant expression that is the size of
an array of char large enough to hold a temporary file name string
generated by the tmpnam
function;
SEEK_CUR SEEK_END SEEK_SET
which expand to distinct integral constant expressions, suitable for
use as the third argument to the fseek
function;
TMP_MAX
which expands to an integral constant expression that is the minimum number of unique file names that shall be generated by the tmpnam function;
stderr stdin stdout
which are expressions of type “pointer to FILE ” that point to the FILE objects associated, respectively, with the standard error, input, and output streams.
Forward references: files (4.9.3), the fseek
function (4.9.9.2),
streams (4.9.2), the tmpnam
function (4.9.4.4).
Input and output, whether to or from physical devices such as terminals and tape drives, or whether to or from files supported on structured storage devices, are mapped into logical data streams, whose properties are more uniform than their various inputs and outputs. Two forms of mapping are supported, for text streams and for binary streams.99
A text stream is an ordered sequence of characters composed into lines, each line consisting of zero or more characters plus a terminating new-line character. Whether the last line requires a terminating new-line character is implementation-defined. Characters may have to be added, altered, or deleted on input and output to conform to differing conventions for representing text in the host environment. Thus, there need not be a one-to-one correspondence between the characters in a stream and those in the external representation. Data read in from a text stream will necessarily compare equal to the data that were earlier written out to that stream only if: the data consist only of printable characters and the control characters horizontal tab and new-line; no new-line character is immediately preceded by space characters; and the last character is a new-line character. Whether space characters that are written out immediately before a new-line character appear when read in is implementation-defined.
A binary stream is an ordered sequence of characters that can transparently record internal data. Data read in from a binary stream shall compare equal to the data that were earlier written out to that stream, under the same implementation. Such a stream may, however, have an implementation-defined number of null characters appended.
An implementation shall support text files with lines containing at least 254 characters, including the terminating new-line character. The value of the macro BUFSIZ shall be at least 256.
A stream is associated with an external file (which may be a
physical device) by opening a file, which may involve creating a new
file. Creating an existing file causes its former contents to be
discarded, if necessary, so that it appears as if newly created. If a
file can support positioning requests (such as a disk file, as opposed
to a terminal), then a file position indicator100 associated with
the stream is positioned at the start (character number zero) of the
file, unless the file is opened with append mode in which case it is
implementation-defined whether the file position indicator is
positioned at the beginning or the end of the file. The file position
indicator is maintained by subsequent reads, writes, and positioning
requests, to facilitate an orderly progression through the file. All
input takes place as if characters were read by successive calls to the
fgetc function; all output takes place as if characters were written by
successive calls to the fputc
function.
Binary files are not truncated, except as defined in 4.9.5.3. Whether a write on a text stream causes the associated file to be truncated beyond that point is implementation-defined.
When a stream is unbuffered, characters are intended to appear from the source or at the destination as soon as possible. Otherwise characters may be accumulated and transmitted to or from the host environment as a block. When a stream is fully buffered, characters are intended to be transmitted to or from the host environment as a block when a buffer is filled. When a stream is line buffered, characters are intended to be transmitted to or from the host environment as a block when a new-line character is encountered. Furthermore, characters are intended to be transmitted as a block to the host environment when a buffer is filled, when input is requested on an unbuffered stream, or when input is requested on a line buffered stream that requires the transmission of characters from the host environment. Support for these characteristics is implementation-defined, and may be affected via the setbuf and setvbuf functions.
A file may be disassociated from its controlling stream by closing the file. Output streams are flushed (any unwritten buffer contents are transmitted to the host environment) before the stream is disassociated from the file. The value of a pointer to a FILE object is indeterminate after the associated file is closed (including the standard text streams). Whether a file of zero length (on which no characters have been written by an output stream) actually exists is implementation-defined.
The file may be subsequently reopened, by the same or another
program execution, and its contents reclaimed or modified (if it can
be repositioned at its start). If the main
function returns to its
original caller, or if the exit
function is called, all open files are
closed (hence all output streams are flushed) before program
termination. Other paths to program termination, such as calling the
abort function, need not close all files properly.
The address of the FILE object used to control a stream may be significant; a copy of a FILE object may not necessarily serve in place of the original.
At program startup, three text streams are predefined and need not be opened explicitly — standard input (for reading conventional input), standard output (for writing conventional output), and standard error (for writing diagnostic output). When opened, the standard error stream is not fully buffered; the standard input and standard output streams are fully buffered if and only if the stream can be determined not to refer to an interactive device.
Functions that open additional (nontemporary) files require a file name, which is a string. The rules for composing valid file names are implementation-defined. Whether the same file can be simultaneously open multiple times is also implementation-defined.
The value of the macro FOPEN_MAX shall be at least eight, including the three standard text streams.
Forward references: the exit
function (4.10.4.3), the fgetc
function
(4.9.7.1), the fopen
function (4.9.5.3), the fputc
function
(4.9.7.3), the setbuf
function (4.9.5.5), the setvbuf
function
(4.9.5.6).
remove
function #include <stdio.h>
int remove(const char *filename);
The remove
function causes the file whose name is the string
pointed to by filename to be no longer accessible by that name. A
subsequent attempt to open that file using that name will fail, unless
it is created anew. If the file is open, the behavior of the remove
function is implementation-defined.
The remove
function returns zero if the operation succeeds, nonzero
if it fails.
rename
function #include <stdio.h>
int rename(const char *old, const char *new);
The rename
function causes the file whose name is the string
pointed to by old to be henceforth known by the name given by the
string pointed to by new. The file named old is effectively removed.
If a file named by the string pointed to by new exists prior to the
call to the rename
function, the behavior is implementation-defined.
The rename
function returns zero if the operation succeeds, nonzero
if it fails,101 in which case if the file existed previously it is
still known by its original name.
tmpfile
function #include <stdio.h>
FILE *tmpfile(void);
The tmpfile
function creates a temporary binary file that will
automatically be removed when it is closed or at program termination.
If the program terminates abnormally, whether an open temporary file
is removed is implementation-defined. The file is opened for update
with wb+ mode.
The tmpfile
function returns a pointer to the stream of the file
that it created. If the file cannot be created, the tmpfile
function
returns a null pointer.
Forward references: the fopen
function (4.9.5.3).
tmpnam
function #include <stdio.h>
char *tmpnam(char *s);
The tmpnam
function generates a string that is a valid file name
and that is not the same as the name of an existing file.102
The tmpnam
function generates a different string each time it is
called, up to TMP_MAX times. If it is called more than TMP_MAX times,
the behavior is implementation-defined.
The implementation shall behave as if no library function calls the tmpnam function.
If the argument is a null pointer, the tmpnam
function leaves its
result in an internal static object and returns a pointer to that
object. Subsequent calls to the tmpnam
function may modify the same
object. If the argument is not a null pointer, it is assumed to point
to an array of at least L_tmpnam char s; the tmpnam
function writes
its result in that array and returns the argument as its value.
The value of the macro TMP_MAX shall be at least 25.
fclose
function #include <stdio.h>
int fclose(FILE *stream);
The fclose
function causes the stream pointed to by stream to be
flushed and the associated file to be closed. Any unwritten buffered
data for the stream are delivered to the host environment to be
written to the file; any unread buffered data are discarded. The
stream is disassociated from the file. If the associated buffer was
automatically allocated, it is deallocated.
The fclose
function returns zero if the stream was successfully
closed, or EOF if any errors were detected.
fflush
function #include <stdio.h>
int fflush(FILE *stream);
If stream points to an output stream or an update stream in which
the most recent operation was output, the fflush
function causes any
unwritten data for that stream to be delivered to the host environment
to be written to the file; otherwise, the behavior is undefined.
If stream is a null pointer, the fflush
function performs this
flushing action on all streams for which the behavior is defined
above.
The fflush
function returns EOF if a write error occurs, otherwise zero.
Forward references: the ungetc
function (4.9.7.11).
fopen
function #include <stdio.h>
FILE *fopen(const char *filename, const char *mode);
The fopen
function opens the file whose name is the string pointed
to by filename, and associates a stream with it.
The argument mode points to a string beginning with one of the following sequences:103
"r" open text file for reading "w" truncate to zero length or create text file for writing "a" append; open or create text file for writing at end-of-file "rb" open binary file for reading "wb" truncate to zero length or create binary file for writing "ab" append; open or create binary file for writing at end-of-file "r+" open text file for update (reading and writing) "w+" truncate to zero length or create text file for update "a+" append; open or create text file for update, writing at end-of-file "r+b" or "rb+" open binary file for update (reading and writing) "w+b" or "wb+" truncate to zero length or create binary file for update "a+b" or "ab+" append; open or create binary file for update, writing at end-of-file
Opening a file with read mode ('r' as the first character in the mode argument) fails if the file does not exist or cannot be read.
Opening a file with append mode ('a' as the first character in the
mode argument) causes all subsequent writes to the file to be forced
to the then current end-of-file, regardless of intervening calls to
the fseek
function. In some implementations, opening a binary file
with append mode ('b' as the second or third character in the mode
argument) may initially position the file position indicator for the
stream beyond the last data written, because of null character
padding.
When a file is opened with update mode ('+' as the second or third character in the mode argument), both input and output may be performed on the associated stream. However, output may not be directly followed by input without an intervening call to the fflush function or to a file positioning function ( fseek, fsetpos, or rewind ), and input may not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file. Opening a file with update mode may open or create a binary stream in some implementations.
When opened, a stream is fully buffered if and only if it can be determined not to refer to an interactive device. The error and end-of-file indicators for the stream are cleared.
The fopen
function returns a pointer to the object controlling the
stream. If the open operation fails, fopen returns a null pointer.
Forward references: file positioning functions (4.9.9).
freopen
function #include <stdio.h>
FILE *freopen(const char *filename, const char *mode,
FILE *stream);
The freopen
function opens the file whose name is the string
pointed to by filename and associates the stream pointed to by stream
with it. The mode argument is used just as in the fopen
function.104
The freopen
function first attempts to close any file that is
associated with the specified stream. Failure to close the file
successfully is ignored. The error and end-of-file indicators for the
stream are cleared.
The freopen
function returns a null pointer if the open operation
fails. Otherwise, freopen returns the value of stream.
setbuf
function #include <stdio.h>
void setbuf(FILE *stream, char *buf);
Except that it returns no value, the setbuf
function is equivalent
to the setvbuf
function invoked with the values _IOFBF for mode and
BUFSIZ for size, or (if buf is a null pointer), with the value _IONBF
for mode.
The setbuf
function returns no value.
Forward references: the setvbuf
function (4.9.5.6).
setvbuf
function #include <stdio.h>
int setvbuf(FILE *stream, char *buf, int mode, size_t size);
The setvbuf
function may be used after the stream pointed to by
stream has been associated with an open file but before any other
operation is performed on the stream. The argument mode determines
how stream will be buffered, as follows: _IOFBF causes input/output to
be fully buffered; _IOLBF causes output to be line buffered; _IONBF
causes input/output to be unbuffered. If buf is not a null pointer,
the array it points to may be used instead of a buffer allocated by
the setvbuf
function.105 The argument size specifies the size of the
array. The contents of the array at any time are indeterminate.
The setvbuf
function returns zero on success, or nonzero if an
invalid value is given for mode or if the request cannot be honored.
fprintf
function #include <stdio.h>
int fprintf(FILE *stream, const char *format, ...);
The fprintf
function writes output to the stream pointed to by
stream, under control of the string pointed to by format that
specifies how subsequent arguments are converted for output. If there
are insufficient arguments for the format, the behavior is undefined.
If the format is exhausted while arguments remain, the excess
arguments are evaluated (as always) but are otherwise ignored. The
fprintf function returns when the end of the format string is
encountered.
The format shall be a multibyte character sequence, beginning and ending in its initial shift state. The format is composed of zero or more directives: ordinary multibyte characters (not % ), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the character %. After the %, the following appear in sequence:
A field width or precision, or both, may be indicated by an asterisk * instead of a digit string. In this case, an int argument supplies the field width or precision. The arguments specifying field width or precision, or both, shall appear (in that order) before the argument (if any) to be converted. A negative field width argument is taken as a - flag followed by a positive field width. A negative precision argument is taken as if it were missing.
The flag characters and their meanings are
- The result of the conversion will be left-justified within the field.
+ The result of a signed conversion will always begin with a plus or minus sign.
space If the first character of a signed conversion is not a sign, or if a signed conversion results in no characters, a space will be prepended to the result. If the space and + flags both appear, the space flag will be ignored.
# The result is to be converted to an “alternate form.” For o conversion, it increases the precision to force the first digit of the result to be a zero. For x (or X ) conversion, a nonzero result will have 0x (or 0X ) prepended to it. For e , E , f , g , and G conversions, the result will always contain a decimal-point character, even if no digits follow it (normally, a decimal-point character appears in the result of these conversions only if a digit follows it). For g and G conversions, trailing zeros will not be removed from the result. For other conversions, the behavior is undefined.
0 For d, i, o, u, x, X, e, E, f, g and G conversions, leading zeros (following any indication of sign or base) are used to pad to the field width; no space padding is performed. If the 0 and - flags both appear, the 0 flag will be ignored. For d, i, o, u, x and X conversions, if a precision is specified, the 0 flag will be ignored. For other conversions, the behavior is undefined.
The conversion specifiers and their meanings are
d, i, o, u, x, X The int argument is converted to signed decimal ( d or i ), unsigned octal ( o ), unsigned decimal ( u ), or unsigned hexadecimal notation ( x or X ); the letters abcdef are used for x conversion and the letters ABCDEF for X conversion. The precision specifies the minimum number of digits to appear; if the value being converted can be represented in fewer digits, it will be expanded with leading zeros. The default precision is 1. The result of converting a zero value with an explicit precision of zero is no characters.
f The double argument is converted to decimal notation in the style [-]ddd.ddd , where the number of digits after the decimal-point character is equal to the precision specification. If the precision is missing, it is taken as 6; if the precision is explicitly zero, no decimal-point character appears. If a decimal-point character appears, at least one digit appears before it. The value is rounded to the appropriate number of digits.
e, E The double argument is converted in the style [-]d.ddde+- dd , where there is one digit before the decimal-point character (which is nonzero if the argument is nonzero) and the number of digits after it is equal to the precision; if the precision is missing, it is taken as 6; if the precision is zero, no decimal-point character appears. The value is rounded to the appropriate number of digits. The E conversion specifier will produce a number with E instead of e introducing the exponent. The exponent always contains at least two digits. If the value is zero, the exponent is zero.
g, G The double argument is converted in style f or e (or in style E in the case of a G conversion specifier), with the precision specifying the number of significant digits. If an explicit precision is zero, it is taken as 1. The style used depends on the value converted; style e will be used only if the exponent resulting from such a conversion is less than -4 or greater than or equal to the precision. Trailing zeros are removed from the fractional portion of the result; a decimal-point character appears only if it is followed by a digit.
c The int argument is converted to an unsigned char , and the resulting character is written.
s The argument shall be a pointer to an array of character type.107 Characters from the array are written up to (but not including) a terminating null character; if the precision is specified, no more than that many characters are written. If the precision is not specified or is greater than the size of the array, the array shall contain a null character.
p The argument shall be a pointer to void . The value of the pointer is converted to a sequence of printable characters, in an implementation-defined manner.
n The argument shall be a pointer to an integer into which is written the number of characters written to the output stream so far by this call to fprintf . No argument is converted.
% A % is written. No argument is converted. The complete conversion specification shall be %% .
If a conversion specification is invalid, the behavior is undefined.108
If any argument is, or points to, a union or an aggregate (except for an array of character type using %s conversion, or a pointer cast to be a pointer to void using %p conversion), the behavior is undefined.
In no case does a nonexistent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.
The fprintf
function returns the number of characters transmitted,
or a negative value if an output error occurred.
The minimum value for the maximum number of characters produced by any single conversion shall be 509.
To print a date and time in the form “Sunday, July 3, 10:02,” where weekday and month are pointers to strings:
#include <stdio.h>
fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
weekday, month, day, hour, min);
To print PI to five decimal places:
#include <math.h>
#include <stdio.h>
fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));
fscanf
function #include <stdio.h>
int fscanf(FILE *stream, const char *format, ...);
The fscanf
function reads input from the stream pointed to by
stream, under control of the string pointed to by format that
specifies the admissible input sequences and how they are to be
converted for assignment, using subsequent arguments as pointers to
the objects to receive the converted input. If there are insufficient
arguments for the format, the behavior is undefined. If the format is
exhausted while arguments remain, the excess arguments are evaluated
(as always) but are otherwise ignored.
The format shall be a multibyte character sequence, beginning and ending in its initial shift state. The format is composed of zero or more directives: one or more white-space characters; an ordinary multibyte character (not % ); or a conversion specification. Each conversion specification is introduced by the character %. After the %, the following appear in sequence:
The fscanf
function executes each directive of the format in turn.
If a directive fails, as detailed below, the fscanf
function returns.
Failures are described as input failures (due to the unavailability of
input characters), or matching failures (due to inappropriate input).
A directive composed of white space is executed by reading input up to the first non-white-space character (which remains unread), or until no more characters can be read.
A directive that is an ordinary multibyte character is executed by reading the next characters of the stream. If one of the characters differs from one comprising the directive, the directive fails, and the differing and subsequent characters remain unread.
A directive that is a conversion specification defines a set of matching input sequences, as described below for each specifier. A conversion specification is executed in the following steps:
Input white-space characters (as specified by the isspace
function)
are skipped, unless the specification includes a [, c, or n
specifier.
An input item is read from the stream, unless the specification includes an n specifier. An input item is defined as the longest sequence of input characters (up to any specified maximum field width) which is an initial subsequence of a matching sequence. The first character, if any, after the input item remains unread. If the length of the input item is zero, the execution of the directive fails: this condition is a matching failure, unless an error prevented input from the stream, in which case it is an input failure.
Except in the case of a % specifier, the input item (or, in the case of a %n directive, the count of input characters) is converted to a type appropriate to the conversion specifier. If the input item is not a matching sequence, the execution of the directive fails: this condition is a matching failure. Unless assignment suppression was indicated by a *, the result of the conversion is placed in the object pointed to by the first argument following the format argument that has not already received a conversion result. If this object does not have an appropriate type, or if the result of the conversion cannot be represented in the space provided, the behavior is undefined.
The following conversion specifiers are valid:
d Matches an optionally signed decimal integer, whose format is the
same as expected for the subject sequence of the strtol
function with
the value 10 for the base argument. The corresponding argument shall
be a pointer to integer.
i Matches an optionally signed integer, whose format is the same as
expected for the subject sequence of the strtol
function with the
value 0 for the base argument. The corresponding argument shall be a
pointer to integer.
o Matches an optionally signed octal integer, whose format is the same
as expected for the subject sequence of the strtoul
function with the
value 8 for the base argument. The corresponding argument shall be a
pointer to unsigned integer.
u Matches an optionally signed decimal integer, whose format is the same
as expected for the subject sequence of the strtoul
function with the
value 10 for the base argument. The corresponding argument shall be a
pointer to unsigned integer.
x Matches an optionally signed hexadecimal integer, whose format is the
same as expected for the subject sequence of the strtoul
function with
the value 16 for the base argument. The corresponding argument shall
be a pointer to unsigned integer.
e,f,g Matches an optionally signed floating-point number, whose format is
the same as expected for the subject string of the strtod
function.
The corresponding argument shall be a pointer to floating.
s Matches a sequence of non-white-space characters. The corresponding argument shall be a pointer to the initial character of an array large enough to accept the sequence and a terminating null character, which will be added automatically.
[ Matches a nonempty sequence of characters from a set of expected characters (the scanset ). The corresponding argument shall be a pointer to the initial character of an array large enough to accept the sequence and a terminating null character, which will be added automatically. The conversion specifier includes all subsequent characters in the format string, up to and including the matching right bracket ( ] ). The characters between the brackets (the scanlist ) comprise the scanset, unless the character after the left bracket is a circumflex ( ^ ), in which case the scanset contains all characters that do not appear in the scanlist between the circumflex and the right bracket. As a special case, if the conversion specifier begins with [] or [^] , the right bracket character is in the scanlist and the next right bracket character is the matching right bracket that ends the specification. If a - character is in the scanlist and is not the first, nor the second where the first character is a ^ , nor the last character, the behavior is implementation-defined.
c Matches a sequence of characters of the number specified by the field width (1 if no field width is present in the directive). The corresponding argument shall be a pointer to the initial character of an array large enough to accept the sequence. No null character is added.
p Matches an implementation-defined set of sequences, which should be
the same as the set of sequences that may be produced by the %p
conversion of the fprintf
function. The corresponding argument shall
be a pointer to a pointer to void . The interpretation of the input
item is implementation-defined; however, for any input item other than
a value converted earlier during the same program execution, the
behavior of the %p conversion is undefined.
n No input is consumed. The corresponding argument shall be a pointer
to integer into which is to be written the number of characters read
from the input stream so far by this call to the fscanf
function.
Execution of a %n directive does not increment the assignment count
returned at the completion of execution of the fscanf
function.
% Matches a single % ; no conversion or assignment occurs. The complete conversion specification shall be %% .
If a conversion specification is invalid, the behavior is undefined.110
The conversion specifiers E, G, and X are also valid and behave the same as, respectively, e, g, and x.
If end-of-file is encountered during input, conversion is terminated. If end-of-file occurs before any characters matching the current directive have been read (other than leading white space, where permitted), execution of the current directive terminates with an input failure; otherwise, unless execution of the current directive is terminated with a matching failure, execution of the following directive (if any) is terminated with an input failure.
If conversion terminates on a conflicting input character, the offending input character is left unread in the input stream. Trailing white space (including new-line characters) is left unread unless matched by a directive. The success of literal matches and suppressed assignments is not directly determinable other than via the %n directive.
The fscanf
function returns the value of the macro EOF if an input
failure occurs before any conversion. Otherwise, the fscanf
function
returns the number of input items assigned, which can be fewer than
provided for, or even zero, in the event of an early matching failure.
The call:
#include <stdio.h>
int n, i; float x; char name[50];
n = fscanf(stdin, "%d%f%s", &i, &x, name);
with the input line:
25 54.32E-1 thompson
will assign to n the value 3, to i the value 25, to x the value 5.432, and name will contain thompson\0. Or:
#include <stdio.h>
int i; float x; char name[50];
fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
with input:
56789 0123 56a72
will assign to i the value 56 and to x the value 789.0, will skip 0123, and name will contain 56\0. The next character read from the input stream will be a.
To accept repeatedly from stdin a quantity, a unit of measure and an item name:
#include <stdio.h>
int count; float quant; char units[21], item[21];
while (!feof(stdin) && !ferror(stdin)) {
count = fscanf(stdin, "%f%20s of %20s",
&quant, units, item);
fscanf(stdin,"%*[^\n]");
}
If the stdin stream contains the following lines:
2 quarts of oil -12.8degrees Celsius lots of luck 10.0LBS of fertilizer 100ergs of energy
the execution of the above example will be equivalent to the following assignments:
quant = 2; strcpy(units, "quarts"); strcpy(item, "oil"); count = 3; quant = -12.8; strcpy(units, "degrees"); count = 2; /* "C" fails to match "o" */ count = 0; /* "l" fails to match "%f" */ quant = 10.0; strcpy(units, "LBS"); strcpy(item, "fertilizer"); count = 3; count = 0; /* "100e" fails to match "%f" */ count = EOF;
Forward references: the strtod
function (4.10.1.4), the strtol
function (4.10.1.5), the strtoul
function (4.10.1.6).
printf
function #include <stdio.h>
int printf(const char *format, ...);
The printf
function is equivalent to fprintf with the argument
stdout interposed before the arguments to printf.
The printf
function returns the number of characters transmitted,
or a negative value if an output error occurred.
scanf
function #include <stdio.h>
int scanf(const char *format, ...);
The scanf
function is equivalent to fscanf with the argument stdin
interposed before the arguments to scanf.
The scanf
function returns the value of the macro EOF if an input
failure occurs before any conversion. Otherwise, the scanf
function
returns the number of input items assigned, which can be fewer than
provided for, or even zero, in the event of an early matching failure.
sprintf
function #include <stdio.h>
int sprintf(char *s, const char *format, ...);
The sprintf
function is equivalent to fprintf, except that the
argument s specifies an array into which the generated output is to be
written, rather than to a stream. A null character is written at the
end of the characters written; it is not counted as part of the
returned sum. If copying takes place between objects that overlap,
the behavior is undefined.
The sprintf
function returns the number of characters written in
the array, not counting the terminating null character.
sscanf
function #include <stdio.h>
int sscanf(const char *s, const char *format, ...);
The sscanf
function is equivalent to fscanf, except that the
argument s specifies a string from which the input is to be obtained,
rather than from a stream. Reaching the end of the string is
equivalent to encountering end-of-file for the fscanf
function. If
copying takes place between objects that overlap, the behavior is
undefined.
The sscanf
function returns the value of the macro EOF if an input
failure occurs before any conversion. Otherwise, the sscanf
function
returns the number of input items assigned, which can be fewer than
provided for, or even zero, in the event of an early matching failure.
vfprintf
function #include <stdarg.h>
#include <stdio.h>
int vfprintf(FILE *stream, const char *format, va_list arg);
The vfprintf
function is equivalent to fprintf, with the variable
argument list replaced by arg, which has been initialized by the
va_start macro (and possibly subsequent va_arg calls). The vfprintf
function does not invoke the va_end
macro.
The vfprintf
function returns the number of characters transmitted,
or a negative value if an output error occurred.
The following shows the use of the vfprintf
function in a general
error-reporting routine.
#include <stdarg.h>
#include <stdio.h>
void error(char *function_name, char *format, ...) { va_list args;
va_start(args, format); /* print out name of function causing error */ fprintf(stderr, "ERROR in %s: ", function_name); /* print out remainder of message */ vfprintf(stderr, format, args); va_end(args); }
vprintf
function #include <stdarg.h>
#include <stdio.h>
int vprintf(const char *format, va_list arg);
The vprintf
function is equivalent to printf, with the variable
argument list replaced by arg, which has been initialized by the
va_start macro (and possibly subsequent va_arg calls). The vprintf
function does not invoke the va_end
macro.111
The vprintf
function returns the number of characters transmitted,
or a negative value if an output error occurred.
vsprintf
function #include <stdarg.h>
#include <stdio.h>
int vsprintf(char *s, const char *format, va_list arg);
The vsprintf
function is equivalent to sprintf, with the variable
argument list replaced by arg, which has been initialized by the
va_start macro (and possibly subsequent va_arg calls). The vsprintf
function does not invoke the va_end
macro.111 If copying takes place
between objects that overlap, the behavior is undefined.
The vsprintf
function returns the number of characters written in
the array, not counting the terminating null character.
fgetc
function #include <stdio.h>
int fgetc(FILE *stream);
The fgetc
function obtains the next character (if present) as an
unsigned char converted to an int, from the input stream pointed to
by stream, and advances the associated file position indicator for
the stream (if defined).
The fgetc
function returns the next character from the input stream
pointed to by stream. If the stream is at end-of-file, the
end-of-file indicator for the stream is set and fgetc returns EOF.
If a read error occurs, the error indicator for the stream is set and
fgetc returns EOF.112
fgets
function #include <stdio.h>
char *fgets(char *s, int n, FILE *stream);
The fgets
function reads at most one less than the number of
characters specified by n from the stream pointed to by stream into
the array pointed to by s. No additional characters are read after a
new-line character (which is retained) or after end-of-file. A null
character is written immediately after the last character read into
the array.
The fgets
function returns s if successful. If end-of-file is
encountered and no characters have been read into the array, the
contents of the array remain unchanged and a null pointer is returned.
If a read error occurs during the operation, the array contents are
indeterminate and a null pointer is returned.
fputc
function #include <stdio.h>
int fputc(int c, FILE *stream);
The fputc
function writes the character specified by c (converted
to an unsigned char ) to the output stream pointed to by stream, at
the position indicated by the associated file position indicator for
the stream (if defined), and advances the indicator appropriately. If
the file cannot support positioning requests, or if the stream was
opened with append mode, the character is appended to the output
stream.
The fputc
function returns the character written. If a write error
occurs, the error indicator for the stream is set and fputc returns EOF.
fputs
function #include <stdio.h>
int fputs(const char *s, FILE *stream);
The fputs
function writes the string pointed to by s to the stream
pointed to by stream. The terminating null character is not written.
The fputs
function returns EOF if a write error occurs; otherwise
it returns a nonnegative value.
getc
function #include <stdio.h>
int getc(FILE *stream);
The getc
function is equivalent to fgetc, except that if it is
implemented as a macro, it may evaluate stream more than once, so the
argument should never be an expression with side effects.
The getc
function returns the next character from the input stream
pointed to by stream. If the stream is at end-of-file, the
end-of-file indicator for the stream is set and getc returns EOF. If
a read error occurs, the error indicator for the stream is set and
getc returns EOF.
getchar
function #include <stdio.h>
int getchar(void);
The getchar
function is equivalent to getc with the argument stdin.
The getchar
function returns the next character from the input
stream pointed to by stdin. If the stream is at end-of-file, the
end-of-file indicator for the stream is set and getchar returns EOF.
If a read error occurs, the error indicator for the stream is set and
getchar returns EOF.
gets
function #include <stdio.h>
char *gets(char *s);
The gets
function reads characters from the input stream pointed to
by stdin, into the array pointed to by s, until end-of-file is
encountered or a new-line character is read. Any new-line character
is discarded, and a null character is written immediately after the
last character read into the array.
The gets
function returns s if successful. If end-of-file is
encountered and no characters have been read into the array, the
contents of the array remain unchanged and a null pointer is returned.
If a read error occurs during the operation, the array contents are
indeterminate and a null pointer is returned.
putc
function #include <stdio.h>
int putc(int c, FILE *stream);
The putc
function is equivalent to fputc, except that if it is
implemented as a macro, it may evaluate stream more than once, so the
argument should never be an expression with side effects.
The putc
function returns the character written. If a write error
occurs, the error indicator for the stream is set and putc returns EOF.
putchar
function #include <stdio.h>
int putchar(int c);
The putchar
function is equivalent to putc with the second argument
stdout.
The putchar
function returns the character written. If a write
error occurs, the error indicator for the stream is set and putchar
returns EOF.
puts
function #include <stdio.h>
int puts(const char *s);
The puts
function writes the string pointed to by s to the stream
pointed to by stdout, and appends a new-line character to the output.
The terminating null character is not written.
The puts
function returns EOF if a write error occurs; otherwise it
returns a nonnegative value.
ungetc
function #include <stdio.h>
int ungetc(int c, FILE *stream);
The ungetc
function pushes the character specified by c (converted
to an unsigned char ) back onto the input stream pointed to by stream.
The pushed-back characters will be returned by subsequent reads on
that stream in the reverse order of their pushing. A successful
intervening call (with the stream pointed to by stream ) to a file
positioning function ( fseek, fsetpos, or rewind ) discards any
pushed-back characters for the stream. The external storage
corresponding to the stream is unchanged.
One character of pushback is guaranteed. If the ungetc
function is
called too many times on the same stream without an intervening read
or file positioning operation on that stream, the operation may fail.
If the value of c equals that of the macro EOF, the operation fails and the input stream is unchanged.
A successful call to the ungetc
function clears the end-of-file
indicator for the stream. The value of the file position indicator
for the stream after reading or discarding all pushed-back characters
shall be the same as it was before the characters were pushed back.
For a text stream, the value of its file position indicator after a
successful call to the ungetc
function is unspecified until all
pushed-back characters are read or discarded. For a binary stream,
its file position indicator is decremented by each successful call to
the ungetc
function; if its value was zero before a call, it is
indeterminate after the call.
The ungetc
function returns the character pushed back after
conversion, or EOF if the operation fails.
Forward references: file positioning functions (4.9.9).
fread
function #include <stdio.h>
size_t fread(void *ptr, size_t size, size_t nmemb,
FILE *stream);
The fread
function reads, into the array pointed to by ptr, up to
nmemb members whose size is specified by size, from the stream
pointed to by stream. The file position indicator for the stream (if
defined) is advanced by the number of characters successfully read.
If an error occurs, the resulting value of the file position indicator
for the stream is indeterminate. If a partial member is read, its
value is indeterminate.
The fread
function returns the number of members successfully read,
which may be less than nmemb if a read error or end-of-file is
encountered. If size or nmemb is zero, fread returns zero and the
contents of the array and the state of the stream remain unchanged.
fwrite
function #include <stdio.h>
size_t fwrite(const void *ptr, size_t size, size_t nmemb,
FILE *stream);
The fwrite
function writes, from the array pointed to by ptr, up
to nmemb members whose size is specified by size, to the stream
pointed to by stream. The file position indicator for the stream (if
defined) is advanced by the number of characters successfully written.
If an error occurs, the resulting value of the file position indicator
for the stream is indeterminate.
The fwrite
function returns the number of members successfully
written, which will be less than nmemb only if a write error is
encountered.
fgetpos
function #include <stdio.h>
int fgetpos(FILE *stream, fpos_t *pos);
The fgetpos
function stores the current value of the file position
indicator for the stream pointed to by stream in the object pointed to
by pos. The value stored contains unspecified information usable by
the fsetpos
function for repositioning the stream to its position at
the time of the call to the fgetpos
function.
If successful, the fgetpos
function returns zero; on failure, the
fgetpos function returns nonzero and stores an implementation-defined
positive value in errno.
Forward references: the fsetpos
function (4.9.9.3).
fseek
function #include <stdio.h>
int fseek(FILE *stream, long int offset, int whence);
The fseek
function sets the file position indicator for the stream
pointed to by stream.
For a binary stream, the new position, measured in characters from the beginning of the file, is obtained by adding offset to the position specified by whence. The specified point is the beginning of the file for SEEK_SET, the current value of the file position indicator for SEEK_CUR, or end-of-file for SEEK_END. A binary stream need not meaningfully support fseek calls with a whence value of SEEK_END.
For a text stream, either offset shall be zero, or offset shall be
a value returned by an earlier call to the ftell
function on the same
stream and whence shall be SEEK_SET.
A successful call to the fseek
function clears the end-of-file
indicator for the stream and undoes any effects of the ungetc
function
on the same stream. After an fseek call, the next operation on an
update stream may be either input or output.
The fseek
function returns nonzero only for a request that cannot
be satisfied.
Forward references: the ftell
function (4.9.9.4).
fsetpos
function #include <stdio.h>
int fsetpos(FILE *stream, const fpos_t *pos);
The fsetpos
function sets the file position indicator for the
stream pointed to by stream according to the value of the object
pointed to by pos, which shall be a value returned by an earlier call
to the fgetpos
function on the same stream.
A successful call to the fsetpos
function clears the end-of-file
indicator for the stream and undoes any effects of the ungetc
function
on the same stream. After an fsetpos call, the next operation on an
update stream may be either input or output.
If successful, the fsetpos
function returns zero; on failure, the
fsetpos function returns nonzero and stores an implementation-defined
positive value in errno.
ftell
function #include <stdio.h>
long int ftell(FILE *stream);
The ftell
function obtains the current value of the file position
indicator for the stream pointed to by stream. For a binary stream,
the value is the number of characters from the beginning of the file.
For a text stream, its file position indicator contains unspecified
information, usable by the fseek
function for returning the file
position indicator for the stream to its position at the time of the
ftell call; the difference between two such return values is not
necessarily a meaningful measure of the number of characters written
or read.
If successful, the ftell
function returns the current value of the
file position indicator for the stream. On failure, the ftell
function returns -1L and stores an implementation-defined positive
value in errno.
rewind
function #include <stdio.h>
void rewind(FILE *stream);
The rewind
function sets the file position indicator for the stream
pointed to by stream to the beginning of the file. It is equivalent to
(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared.
The rewind
function returns no value.
clearerr
function #include <stdio.h>
void clearerr(FILE *stream);
The clearerr
function clears the end-of-file and error indicators
for the stream pointed to by stream.
The clearerr
function returns no value.
feof
function #include <stdio.h>
int feof(FILE *stream);
The feof
function tests the end-of-file indicator for the stream
pointed to by stream.
The feof
function returns nonzero if and only if the end-of-file
indicator is set for stream.
ferror
function #include <stdio.h>
int ferror(FILE *stream);
The ferror
function tests the error indicator for the stream
pointed to by stream.
The ferror
function returns nonzero if and only if the error
indicator is set for stream.
perror
function #include <stdio.h>
void perror(const char *s);
The perror
function maps the error number in the integer expression
errno to an error message. It writes a sequence of characters to the
standard error stream thus: first (if s is not a null pointer and the
character pointed to by s is not the null character), the string
pointed to by s followed by a colon and a space; then an appropriate
error message string followed by a new-line character. The contents
of the error message strings are the same as those returned by the
strerror function with argument errno, which are
implementation-defined.
The perror
function returns no value.
Forward references: the strerror
function (4.11.6.2).
<stdlib.h>
The header <stdlib.h>
declares four types and several functions of
general utility, and defines several macros.113
The types declared are size_t and wchar_t (both described in 4.1.5),
div_t
which is a structure type that is the type of the value returned by
the div
function, and
ldiv_t
which is a structure type that is the type of the value returned by
the ldiv
function.
The macros defined are NULL (described in 4.1.5);
EXIT_FAILURE
and
EXIT_SUCCESS
which expand to integral expressions that may be used as the argument
to the exit
function to return unsuccessful or successful termination
status, respectively, to the host environment;
RAND_MAX
which expands to an integral constant expression, the value of which
is the maximum value returned by the rand
function; and
MB_CUR_MAX
which expands to a positive integer expression whose value is the maximum number of bytes in a multibyte character for the extended character set specified by the current locale (category LC_CTYPE ), and whose value is never greater than MB_LEN_MAX.
The functions atof, atoi, and atol need not affect the value of the integer expression errno on an error. If the value of the result cannot be represented, the behavior is undefined.
atof
function #include <stdlib.h>
double atof(const char *nptr);
The atof
function converts the initial portion of the string
pointed to by nptr to double representation. Except for the behavior
on error, it is equivalent to
strtod(nptr, (char **)NULL)
The atof
function returns the converted value.
Forward references: the strtod
function (4.10.1.4).
atoi
function #include <stdlib.h>
int atoi(const char *nptr);
The atoi
function converts the initial portion of the string
pointed to by nptr to int representation. Except for the behavior on
error, it is equivalent to
(int)strtol(nptr, (char **)NULL, 10)
The atoi
function returns the converted value.
Forward references: the strtol
function (4.10.1.5).
atol
function #include <stdlib.h>
long int atol(const char *nptr);
The atol
function converts the initial portion of the string
pointed to by nptr to long int representation. Except for the
behavior on error, it is equivalent to
strtol(nptr, (char **)NULL, 10)
The atol
function returns the converted value.
Forward references: the strtol
function (4.10.1.5).
strtod
function #include <stdlib.h>
double strtod(const char *nptr, char **endptr);
The strtod
function converts the initial portion of the string
pointed to by nptr to double representation. First it decomposes the
input string into three parts: an initial, possibly empty, sequence of
white-space characters (as specified by the isspace
function), a
subject sequence resembling a floating-point constant; and a final
string of one or more unrecognized characters, including the
terminating null character of the input string. Then it attempts to
convert the subject sequence to a floating-point number, and returns
the result.
The expected form of the subject sequence is an optional plus or minus sign, then a nonempty sequence of digits optionally containing a decimal-point character, then an optional exponent part as defined in 3.1.3.1, but no floating suffix. The subject sequence is defined as the longest subsequence of the input string, starting with the first non-white-space character, that is an initial subsequence of a sequence of the expected form. The subject sequence contains no characters if the input string is empty or consists entirely of white space, or if the first non-white-space character is other than a sign, a digit, or a decimal-point character.
If the subject sequence has the expected form, the sequence of characters starting with the first digit or the decimal-point character (whichever occurs first) is interpreted as a floating constant according to the rules of 3.1.3.1, except that the decimal-point character is used in place of a period, and that if neither an exponent part nor a decimal-point character appears, a decimal point is assumed to follow the last digit in the string. If the subject sequence begins with a minus sign, the value resulting from the conversion is negated. A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
In other than the C locale, additional implementation-defined subject sequence forms may be accepted.
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
The strtod
function returns the converted value, if any. If no
conversion could be performed, zero is returned. If the correct value
would cause overflow, plus or minus HUGE_VAL is returned (according to
the sign of the value), and the value of the macro ERANGE is stored in
errno. If the correct value would cause underflow, zero is returned
and the value of the macro ERANGE is stored in errno.
strtol
function #include <stdlib.h>
long int strtol(const char *nptr, char **endptr, int base);
The strtol
function converts the initial portion of the string
pointed to by nptr to long int representation. First it decomposes
the input string into three parts: an initial, possibly empty,
sequence of white-space characters (as specified by the isspace
function), a subject sequence resembling an integer represented in
some radix determined by the value of base, and a final string of one
or more unrecognized characters, including the terminating null
character of the input string. Then it attempts to convert the
subject sequence to an integer, and returns the result.
If the value of base is zero, the expected form of the subject sequence is that of an integer constant as described in 3.1.3.2, optionally preceded by a plus or minus sign, but not including an integer suffix. If the value of base is between 2 and 36, the expected form of the subject sequence is a sequence of letters and digits representing an integer with the radix specified by base, optionally preceded by a plus or minus sign, but not including an integer suffix. The letters from a (or A ) through z (or Z ) are ascribed the values 10 to 35; only letters whose ascribed values are less than that of base are permitted. If the value of base is 16, the characters 0x or 0X may optionally precede the sequence of letters and digits, following the sign if present.
The subject sequence is defined as the longest subsequence of the input string, starting with the first non-white-space character, that is an initial subsequence of a sequence of the expected form. The subject sequence contains no characters if the input string is empty or consists entirely of white space, or if the first non-white-space character is other than a sign or a permissible letter or digit.
If the subject sequence has the expected form and the value of base is zero, the sequence of characters starting with the first digit is interpreted as an integer constant according to the rules of 3.1.3.2. If the subject sequence has the expected form and the value of base is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value as given above. If the subject sequence begins with a minus sign, the value resulting from the conversion is negated. A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
In other than the C locale, additional implementation-defined subject sequence forms may be accepted.
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
The strtol
function returns the converted value, if any. If no
conversion could be performed, zero is returned. If the correct value
would cause overflow, LONG_MAX or LONG_MIN is returned (according to
the sign of the value), and the value of the macro ERANGE is stored in
errno.
strtoul
function #include <stdlib.h>
unsigned long int strtoul(const char *nptr, char **endptr,
int base);
The strtoul
function converts the initial portion of the string
pointed to by nptr to unsigned long int representation. First it
decomposes the input string into three parts: an initial, possibly
empty, sequence of white-space characters (as specified by the isspace
function), a subject sequence resembling an unsigned integer
represented in some radix determined by the value of base, and a
final string of one or more unrecognized characters, including the
terminating null character of the input string. Then it attempts to
convert the subject sequence to an unsigned integer, and returns the
result.
If the value of base is zero, the expected form of the subject sequence is that of an integer constant as described in 3.1.3.2, optionally preceded by a plus or minus sign, but not including an integer suffix. If the value of base is between 2 and 36, the expected form of the subject sequence is a sequence of letters and digits representing an integer with the radix specified by base, optionally preceded by a plus or minus sign, but not including an integer suffix. The letters from a (or A ) through z (or Z ) are ascribed the values 10 to 35; only letters whose ascribed values are less than that of base are permitted. If the value of base is 16, the characters 0x or 0X may optionally precede the sequence of letters and digits, following the sign if present.
The subject sequence is defined as the longest subsequence of the input string, starting with the first non-white-space character, that is an initial subsequence of a sequence of the expected form. The subject sequence contains no characters if the input string is empty or consists entirely of white space, or if the first non-white-space character is other than a sign or a permissible letter or digit.
If the subject sequence has the expected form and the value of base is zero, the sequence of characters starting with the first digit is interpreted as an integer constant according to the rules of 3.1.3.2. If the subject sequence has the expected form and the value of base is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value as given above. If the subject sequence begins with a minus sign, the value resulting from the conversion is negated. A pointer to the final string is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
In other than the C locale, additional implementation-defined subject sequence forms may be accepted.
If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of nptr is stored in the object pointed to by endptr, provided that endptr is not a null pointer.
The strtoul
function returns the converted value, if any. If no
conversion could be performed, zero is returned. If the correct value
would cause overflow, ULONG_MAX is returned, and the value of the
macro ERANGE is stored in errno.
rand
function #include <stdlib.h>
int rand(void);
The rand
function computes a sequence of pseudo-random integers in
the range 0 to RAND_MAX.
The implementation shall behave as if no library function calls the rand function.
The rand
function returns a pseudo-random integer.
The value of the RAND_MAX
macro shall be at least 32767.
srand
function #include <stdlib.h>
void srand(unsigned int seed);
The srand
function uses the argument as a seed for a new sequence
of pseudo-random numbers to be returned by subsequent calls to rand.
If srand is then called with the same seed value, the sequence of
pseudo-random numbers shall be repeated. If rand is called before any
calls to srand have been made, the same sequence shall be generated as
when srand is first called with a seed value of 1.
The implementation shall behave as if no library function calls the srand function.
The srand
function returns no value.
The following
functions define a portable implementation of rand
and srand. Specifying the semantics makes it possible to determine
reproducibly the behavior of programs that use pseudo-random
sequences. This facilitates the testing of portable applications in
different implementations.
static unsigned long int next = 1;
int rand(void) /* RAND_MAX assumed to be 32767 */ { next = next * 1103515245 + 12345; return (unsigned int)(next/65536) % 32768; }
void srand(unsigned int seed) { next = seed; }
The order and contiguity of storage allocated by successive calls to the calloc, malloc, and realloc functions is unspecified. The pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to a pointer to any type of object and then used to access such an object in the space allocated (until the space is explicitly freed or reallocated). Each such allocation shall yield a pointer to an object disjoint from any other object. The pointer returned points to the start (lowest byte address) of the allocated space. If the space cannot be allocated, a null pointer is returned. If the size of the space requested is zero, the behavior is implementation-defined; the value returned shall be either a null pointer or a unique pointer. The value of a pointer that refers to freed space is indeterminate.
calloc
function #include <stdlib.h>
void *calloc(size_t nmemb, size_t size);
The calloc
function allocates space for an array of nmemb objects,
each of whose size is size. The space is initialized to all bits
zero.114
The calloc
function returns either a null pointer or a pointer to
the allocated space.
free
function #include <stdlib.h>
void free(void *ptr);
The free
function causes the space pointed to by ptr to be
deallocated, that is, made available for further allocation. If ptr
is a null pointer, no action occurs. Otherwise, if the argument does
not match a pointer earlier returned by the calloc, malloc, or
realloc function, or if the space has been deallocated by a call to
free or realloc, the behavior is undefined.
The free
function returns no value.
malloc
function #include <stdlib.h>
void *malloc(size_t size);
The malloc
function allocates space for an object whose size is
specified by size and whose value is indeterminate.
The malloc
function returns either a null pointer or a pointer to
the allocated space.
realloc
function #include <stdlib.h>
void *realloc(void *ptr, size_t size);
The realloc
function changes the size of the object pointed to by
ptr to the size specified by size. The contents of the object shall
be unchanged up to the lesser of the new and old sizes. If the new
size is larger, the value of the newly allocated portion of the object
is indeterminate. If ptr is a null pointer, the realloc
function
behaves like the malloc
function for the specified size. Otherwise,
if ptr does not match a pointer earlier returned by the calloc,
malloc, or realloc function, or if the space has been deallocated by
a call to the free or realloc function, the behavior is undefined. If
the space cannot be allocated, the object pointed to by ptr is
unchanged. If size is zero and ptr is not a null pointer, the object
it points to is freed.
The realloc
function returns either a null pointer or a pointer to
the possibly moved allocated space.
abort
function #include <stdlib.h>
void abort(void);
The abort
function causes abnormal program termination to occur,
unless the signal SIGABRT is being caught and the signal handler does
not return. Whether open output streams are flushed or open streams
closed or temporary files removed is implementation-defined. An
implementation-defined form of the status unsuccessful termination is
returned to the host environment by means of the function call
raise(SIGABRT).
The abort
function cannot return to its caller.
atexit
function #include <stdlib.h>
int atexit(void (*func)(void));
The atexit
function registers the function pointed to by func, to
be called without arguments at normal program termination.
The implementation shall support the registration of at least 32 functions.
The atexit
function returns zero if the registration succeeds,
nonzero if it fails.
Forward references: the exit
function (4.10.4.3).
exit
function #include <stdlib.h>
void exit(int status);
The exit
function causes normal program termination to occur. If
more than one call to the exit
function is executed by a program, the
behavior is undefined.
First, all functions registered by the atexit
function are called,
in the reverse order of their registration.115
Next, all open output streams are flushed, all open streams are
closed, and all files created by the tmpfile
function are removed.
Finally, control is returned to the host environment. If the value of status is zero or EXIT_SUCCESS, an implementation-defined form of the status successful termination is returned. If the value of status is EXIT_FAILURE, an implementation-defined form of the status unsuccessful termination is returned. Otherwise the status returned is implementation-defined.
The exit
function cannot return to its caller.
getenv
function #include <stdlib.h>
char *getenv(const char *name);
The getenv
function searches an environment list, provided by the
host environment, for a string that matches the string pointed to by
name. The set of environment names and the method for altering the
environment list are implementation-defined.
The implementation shall behave as if no library function calls the getenv function.
The getenv
function returns a pointer to a string associated with
the matched list member. The array pointed to shall not be modified
by the program, but may be overwritten by a subsequent call to the
getenv function. If the specified name cannot be found, a null
pointer is returned.
system
function #include <stdlib.h>
int system(const char *string);
The system
function passes the string pointed to by string to the
host environment to be executed by a command processor in an
implementation-defined manner. A null pointer may be used for string
to inquire whether a command processor exists.
If the argument is a null pointer, the system
function returns
nonzero only if a command processor is available. If the argument is
not a null pointer, the system
function returns an
implementation-defined value.
bsearch
function #include <stdlib.h>
void *bsearch(const void *key, const void *base,
size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
The bsearch
function searches an array of nmemb objects, the
initial member of which is pointed to by base, for a member that
matches the object pointed to by key. The size of each member of the
array is specified by size.
The contents of the array shall be in ascending sorted order according to a comparison function pointed to by compar,116 induces which is called with two arguments that point to the key object and to an array member, in that order. The function shall return an integer less than, equal to, or greater than zero if the key object is considered, respectively, to be less than, to match, or to be greater than the array member.
The bsearch
function returns a pointer to a matching member of the
array, or a null pointer if no match is found. If two members compare
as equal, which member is matched is unspecified.
qsort
function #include <stdlib.h>
void qsort(void *base, size_t nmemb, size_t size,
int (*compar)(const void *, const void *));
The qsort
function sorts an array of nmemb objects, the initial
member of which is pointed to by base. The size of each object is
specified by size.
The contents of the array are sorted in ascending order according to a comparison function pointed to by compar, which is called with two arguments that point to the objects being compared. The function shall return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.
If two members compare as equal, their order in the sorted array is unspecified.
The qsort
function returns no value.
abs
function #include <stdlib.h>
int abs(int j);
The abs
function computes the absolute value of an integer j. If
the result cannot be represented, the behavior is undefined.117
The abs
function returns the absolute value.
div
function #include <stdlib.h>
div_t div(int numer, int denom);
The div
function computes the quotient and remainder of the
division of the numerator numer by the denominator denom. If the
division is inexact, the sign of the resulting quotient is that of the
algebraic quotient, and the magnitude of the resulting quotient is the
largest integer less than the magnitude of the algebraic quotient. If
the result cannot be represented, the behavior is undefined;
otherwise, quot * denom + rem shall equal numer.
The div
function returns a structure of type div_t, comprising
both the quotient and the remainder. The structure shall contain the
following members, in either order.
int quot; /* quotient */ int rem; /* remainder */
labs
function #include <stdlib.h>
long int labs(long int j);
The labs
function is similar to the abs
function, except that the
argument and the returned value each have type long int.
ldiv
function #include <stdlib.h>
ldiv_t ldiv(long int numer, long int denom);
The ldiv
function is similar to the div
function, except that the
arguments and the members of the returned structure (which has type
ldiv_t ) all have type long int.
The behavior of the multibyte character functions is affected by the LC_CTYPE category of the current locale. For a state-dependent encoding, each function is placed into its initial state by a call for which its character pointer argument, s, is a null pointer. Subsequent calls with s as other than a null pointer cause the internal state of the function to be altered as necessary. A call with s as a null pointer causes these functions to return a nonzero value if encodings have state dependency, and zero otherwise. After the LC_CTYPE category is changed, the shift state of these functions is indeterminate.
mblen
function #include <stdlib.h>
int mblen(const char *s, size_t n);
If s is not a null pointer, the mblen
function determines the
number of bytes comprising the multibyte character pointed to by s.
Except that the shift state of the mbtowc
function is not affected, it
is equivalent to
mbtowc((wchar_t *)0, s, n);
The implementation shall behave as if no library function calls the mblen function.
If s is a null pointer, the mblen
function returns a nonzero or
zero value, if multibyte character encodings, respectively, do or do
not have state-dependent encodings. If s is not a null pointer, the
mblen function either returns 0 (if s points to the null character),
or returns the number of bytes that comprise the multibyte character
(if the next n or fewer bytes form a valid multibyte character), or
returns -1 (if they do not form a valid multibyte character).
Forward references: the mbtowc
function (4.10.7.2).
mbtowc
function #include <stdlib.h>
int mbtowc(wchar_t *pwc, const char *s, size_t n);
If s is not a null pointer, the mbtowc
function determines the
number of bytes that comprise the multibyte character pointed to by s.
It then determines the code for value of type wchar_t that
corresponds to that multibyte character. (The value of the code
corresponding to the null character is zero.) If the multibyte
character is valid and pwc is not a null pointer, the mbtowc
function
stores the code in the object pointed to by pwc. At most n bytes of
the array pointed to by s will be examined.
The implementation shall behave as if no library function calls the mbtowc function.
If s is a null pointer, the mbtowc
function returns a nonzero or zero
value, if multibyte character encodings, respectively, do or do not
have state-dependent encodings. If s is not a null pointer, the
mbtowc function either returns 0 (if s points to the null character),
or returns the number of bytes that comprise the converted multibyte
character (if the next n or fewer bytes form a valid multibyte
character), or returns -1 (if they do not form a valid multibyte
character).
In no case will the value returned be greater than n or the value
of the MB_CUR_MAX
macro.
wctomb
function #include <stdlib.h>
int wctomb(char *s, wchar_t wchar);
The wctomb
function determines the number of bytes needed to
represent the multibyte character corresponding to the code whose
value is wchar (including any change in shift state). It stores the
multibyte character representation in the array object pointed to by s
(if s is not a null pointer). At most MB_CUR_MAX characters are
stored. If the value of wchar is zero, the wctomb
function is left in
the initial shift state.
The implementation shall behave as if no library function calls the wctomb function.
If s is a null pointer, the wctomb
function returns a nonzero or
zero value, if multibyte character encodings, respectively, do or do
not have state-dependent encodings. If s is not a null pointer, the
wctomb function returns -1 if the value of wchar does not correspond
to a valid multibyte character, or returns the number of bytes that
comprise the multibyte character corresponding to the value of wchar.
In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
The behavior of the multibyte string functions is affected by the LC_CTYPE category of the current locale.
mbstowcs
function #include <stdlib.h>
size_t mbstowcs(wchar_t *pwcs, const char *s, size_t n);
The mbstowcs
function converts a sequence of multibyte characters
that begins in the initial shift state from the array pointed to by s
into a sequence of corresponding codes and stores not more than n
codes into the array pointed to by pwcs. No multibyte characters
that follow a null character (which is converted into a code with
value zero) will be examined or converted. Each multibyte character
is converted as if by a call to the mbtowc
function, except that the
shift state of the mbtowc
function is not affected.
No more than n elements will be modified in the array pointed to by pwcs. If copying takes place between objects that overlap, the behavior is undefined.
If an invalid multibyte character is encountered, the mbstowcs
function returns (size_t)-1. Otherwise, the mbstowcs
function
returns the number of array elements modified, not including a
terminating zero code, if any.118
wcstombs
function #include <stdlib.h>
size_t wcstombs(char *s, const wchar_t *pwcs, size_t n);
The wcstombs
function converts a sequence of codes that correspond
to multibyte characters from the array pointed to by pwcs into a
sequence of multibyte characters that begins in the initial shift
state and stores these multibyte characters into the array pointed to
by s, stopping if a multibyte character would exceed the limit of n
total bytes or if a null character is stored. Each code is converted
as if by a call to the wctomb
function, except that the shift state of
the wctomb
function is not affected.
No more than n bytes will be modified in the array pointed to by s. If copying takes place between objects that overlap, the behavior is undefined.
If a code is encountered that does not correspond to a valid
multibyte character, the wcstombs
function returns (size_t)-1.
Otherwise, the wcstombs
function returns the number of bytes modified,
not including a terminating null character, if any.118
<string.h>
The header <string.h>
declares one type and several functions, and
defines one macro useful for manipulating arrays of character type and
other objects treated as arrays of character type.119 The type is
size_t and the macro is NULL (both described in 4.1.5). Various
methods are used for determining the lengths of the arrays, but in all
cases a char * or void * argument points to the initial (lowest
addressed) character of the array. If an array is accessed beyond the
end of an object, the behavior is undefined.
memcpy
function #include <string.h>
void *memcpy(void *s1, const void *s2, size_t n);
The memcpy
function copies n characters from the object pointed to
by s2 into the object pointed to by s1. If copying takes place
between objects that overlap, the behavior is undefined.
The memcpy
function returns the value of s1.
memmove
function #include <string.h>
void *memmove(void *s1, const void *s2, size_t n);
The memmove
function copies n characters from the object pointed to
by s2 into the object pointed to by s1. Copying takes place as if
the n characters from the object pointed to by s2 are first copied
into a temporary array of n characters that does not overlap the
objects pointed to by s1 and s2, and then the n characters from the
temporary array are copied into the object pointed to by s1.
The memmove
function returns the value of s1.
strcpy
function #include <string.h>
char *strcpy(char *s1, const char *s2);
The strcpy
function copies the string pointed to by s2 (including
the terminating null character) into the array pointed to by s1. If
copying takes place between objects that overlap, the behavior is
undefined.
The strcpy
function returns the value of s1.
strncpy
function #include <string.h>
char *strncpy(char *s1, const char *s2, size_t n);
The strncpy
function copies not more than n characters (characters
that follow a null character are not copied) from the array pointed to
by s2 to the array pointed to by s1.120 If copying takes place
between objects that overlap, the behavior is undefined.
If the array pointed to by s2 is a string that is shorter than n characters, null characters are appended to the copy in the array pointed to by s1, until n characters in all have been written.
The strncpy
function returns the value of s1.
strcat
function #include <string.h>
char *strcat(char *s1, const char *s2);
The strcat
function appends a copy of the string pointed to by s2
(including the terminating null character) to the end of the string
pointed to by s1. The initial character of s2 overwrites the null
character at the end of s1. If copying takes place between objects
that overlap, the behavior is undefined.
The strcat
function returns the value of s1.
strncat
function #include <string.h>
char *strncat(char *s1, const char *s2, size_t n);
The strncat
function appends not more than n characters (a null
character and characters that follow it are not appended) from the
array pointed to by s2 to the end of the string pointed to by s1.
The initial character of s2 overwrites the null character at the end
of s1. A terminating null character is always appended to the
result.121 If copying takes place between objects that overlap, the
behavior is undefined.
The strncat
function returns the value of s1.
Forward references: the strlen
function (4.11.6.3).
The sign of a nonzero value returned by the comparison
functions is
determined by the sign of the difference between the values of the
first pair of characters (both interpreted as unsigned char ) that
differ in the objects being compared.
memcmp
function #include <string.h>
int memcmp(const void *s1, const void *s2, size_t n);
The memcmp
function compares the first n characters of the object
pointed to by s1 to the first n characters of the object pointed to by
s2.122
The memcmp
function returns an integer greater than, equal to, or
less than zero, according as the object pointed to by s1 is greater
than, equal to, or less than the object pointed to by s2.
strcmp
function #include <string.h>
int strcmp(const char *s1, const char *s2);
The strcmp
function compares the string pointed to by s1 to the
string pointed to by s2.
The strcmp
function returns an integer greater than, equal to, or
less than zero, according as the string pointed to by s1 is greater
than, equal to, or less than the string pointed to by s2.
strcoll
function #include <string.h>
int strcoll(const char *s1, const char *s2);
The strcoll
function compares the string pointed to by s1 to the
string pointed to by s2, both interpreted as appropriate to the
LC_COLLATE category of the current locale.
The strcoll
function returns an integer greater than, equal to, or
less than zero, according as the string pointed to by s1 is greater
than, equal to, or less than the string pointed to by s2 when both are
interpreted as appropriate to the current locale.
strncmp
function #include <string.h>
int strncmp(const char *s1, const char *s2, size_t n);
The strncmp
function compares not more than n characters
(characters that follow a null character are not compared) from the
array pointed to by s1 to the array pointed to by s2.
The strncmp
function returns an integer greater than, equal to, or
less than zero, according as the possibly null-terminated array
pointed to by s1 is greater than, equal to, or less than the possibly
null-terminated array pointed to by s2.
strxfrm
function #include <string.h>
size_t strxfrm(char *s1, const char *s2, size_t n);
The strxfrm
function transforms the string pointed to by s2 and
places the resulting string into the array pointed to by s1. The
transformation is such that if the strcmp
function is applied to two
transformed strings, it returns a value greater than, equal to, or
less than zero, corresponding to the result of the strcoll
function
applied to the same two original strings. No more than n characters
are placed into the resulting array pointed to by s1, including the
terminating null character. If n is zero, s1 is permitted to be a
null pointer. If copying takes place between objects that overlap,
the behavior is undefined.
The strxfrm
function returns the length of the transformed string
(not including the terminating null character). If the value returned
is n or more, the contents of the array pointed to by s1 are
indeterminate.
The value of the following expression is the size of the array needed to hold the transformation of the string pointed to by s.
1 + strxfrm(NULL, s, 0)
memchr
function #include <string.h>
void *memchr(const void *s, int c, size_t n);
The memchr
function locates the first occurrence of c (converted to
an unsigned char ) in the initial n characters (each interpreted as
unsigned char ) of the object pointed to by s.
The memchr
function returns a pointer to the located character, or
a null pointer if the character does not occur in the object.
strchr
function #include <string.h>
char *strchr(const char *s, int c);
The strchr
function locates the first occurrence of c (converted to
a char ) in the string pointed to by s. The terminating null
character is considered to be part of the string.
The strchr
function returns a pointer to the located character, or
a null pointer if the character does not occur in the string.
strcspn
function #include <string.h>
size_t strcspn(const char *s1, const char *s2);
The strcspn
function computes the length of the maximum initial
segment of the string pointed to by s1 which consists entirely of
characters not from the string pointed to by s2.
The strcspn
function returns the length of the segment.
strpbrk
function #include <string.h>
char *strpbrk(const char *s1, const char *s2);
The strpbrk
function locates the first occurrence in the string
pointed to by s1 of any character from the string pointed to by s2.
The strpbrk
function returns a pointer to the character, or a null
pointer if no character from s2 occurs in s1.
strrchr
function #include <string.h>
char *strrchr(const char *s, int c);
The strrchr
function locates the last occurrence of c (converted to
a char ) in the string pointed to by s. The terminating null
character is considered to be part of the string.
The strrchr
function returns a pointer to the character, or a null
pointer if c does not occur in the string.
strspn
function #include <string.h>
size_t strspn(const char *s1, const char *s2);
The strspn
function computes the length of the maximum initial
segment of the string pointed to by s1 which consists entirely of
characters from the string pointed to by s2.
The strspn
function returns the length of the segment.
strstr
function #include <string.h>
char *strstr(const char *s1, const char *s2);
The strstr
function locates the first occurrence in the string
pointed to by s1 of the sequence of characters (excluding the
terminating null character) in the string pointed to by s2
The strstr
function returns a pointer to the located string, or a
null pointer if the string is not found. If s2 points to a string
with zero length, the function returns s1.
strtok
function #include <string.h>
char *strtok(char *s1, const char *s2);
A sequence of calls to the strtok
function breaks the string
pointed to by s1 into a sequence of tokens, each of which is delimited
by a character from the string pointed to by s2. The first call in
the sequence has s1 as its first argument, and is followed by calls
with a null pointer as their first argument. The separator string
pointed to by s2 may be different from call to call.
The first call in the sequence searches the string pointed to by s1
for the first character that is not contained in the current separator
string pointed to by s2. If no such character is found, then there
are no tokens in the string pointed to by s1 and the strtok
function
returns a null pointer. If such a character is found, it is the start
of the first token.
The strtok
function then searches from there for a character that
is contained in the current separator string. If no such character is
found, the current token extends to the end of the string pointed to
by s1, and subsequent searches for a token will return a null
pointer. If such a character is found, it is overwritten by a null
character, which terminates the current token. The strtok
function
saves a pointer to the following character, from which the next search
for a token will start.
Each subsequent call, with a null pointer as the value of the first argument, starts searching from the saved pointer and behaves as described above.
The implementation shall behave as if no library function calls the strtok function.
The strtok
function returns a pointer to the first character of a
token, or a null pointer if there is no token.
#include <string.h>
static char str[] = "?a???b,,,#c";
char *t;
t = strtok(str, "?"); /* t points to the token "a" */ t = strtok(NULL, ","); /* t points to the token "??b" */ t = strtok(NULL, "#,"); /* t points to the token "c" */ t = strtok(NULL, "?"); /* t is a null pointer */
memset
function #include <string.h>
void *memset(void *s, int c, size_t n);
The memset
function copies the value of c (converted to an unsigned
char ) into each of the first n characters of the object pointed to by
s.
The memset
function returns the value of s.
strerror
function #include <string.h>
char *strerror(int errnum);
The strerror
function maps the error number in errnum to an error
message string.
The implementation shall behave as if no library function calls the strerror function.
The strerror
function returns a pointer to the string, the contents
of which are implementation-defined. The array pointed to shall not
be modified by the program, but may be overwritten by a subsequent
call to the strerror
function.
strlen
function #include <string.h>
size_t strlen(const char *s);
The strlen
function computes the length of the string pointed to by s.
The strlen
function returns the number of characters that precede
the terminating null character.
<time.h>
The header <time.h>
defines two macros, and declares four types and
several functions for manipulating time. Many functions deal with a
calendar time that represents the current date (according to the
Gregorian calendar) and time. Some functions deal with local time,
which is the calendar time expressed for some specific time zone, and
with Daylight Saving Time, which is a temporary change in the
algorithm for determining local time. The local time zone and
Daylight Saving Time are implementation-defined.
The macros defined are NULL (described in 4.1.5); and
CLK_TCK
which is the number per second of the value returned by the clock
function.
The types declared are size_t (described in 4.1.5);
clock_t
and
time_t
which are arithmetic types capable of representing times; and
struct tm
which holds the components of a calendar time, called the broken-down time. The structure shall contain at least the following members, in any order. The semantics of the members and their normal ranges are expressed in the comments.123
int tm_sec; /* seconds after the minute — [0, 60] */ int tm_min; /* minutes after the hour — [0, 59] */ int tm_hour; /* hours since midnight — [0, 23] */ int tm_mday; /* day of the month — [1, 31] */ int tm_mon; /* months since January — [0, 11] */ int tm_year; /* years since 1900 */ int tm_wday; /* days since Sunday — [0, 6] */ int tm_yday; /* days since January 1 — [0, 365] */ int tm_isdst; /* Daylight Saving Time flag */
The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight Saving Time is not in effect, and negative if the information is not available.
clock
function #include <time.h>
clock_t clock(void);
The clock
function determines the processor time used.
The clock
function returns the implementation's best approximation
to the processor time used by the program since the beginning of an
implementation-defined era related only to the program invocation. To
determine the time in seconds, the value returned by the clock
function should be divided by the value of the macro CLK_TCK. If the
processor time used is not available or its value cannot be
represented, the function returns the value (clock_t)-1.
difftime
function #include <time.h>
double difftime(time_t time1, time_t time0);
The difftime
function computes the difference between two calendar
times: time1 - time0.
The difftime
function returns the difference expressed in seconds
as a double.
mktime
function #include <time.h>
time_t mktime(struct tm *timeptr);
The mktime
function converts the broken-down time, expressed as
local time, in the structure pointed to by timeptr into a calendar
time value with the same encoding as that of the values returned by
the time
function. The original values of the tm_wday and tm_yday
components of the structure are ignored, and the original values of
the other components are not restricted to the ranges indicated
above.124 On successful completion, the values of the tm_wday and
tm_yday components of the structure are set appropriately, and the
other components are set to represent the specified calendar time, but
with their values forced to the ranges indicated above; the final
value of tm_mday is not set until tm_mon and tm_year are determined.
The mktime
function returns the specified calendar time encoded as
a value of type time_t. If the calendar time cannot be represented,
the function returns the value (time_t)-1.
What day of the week is July 4, 2001?
#include <stdio.h>
#include <time.h>
static const char *const wday[] = {
"Sunday", "Monday", "Tuesday", "Wednesday",
"Thursday", "Friday", "Saturday", "-unknown-"
};
struct tm time_str;
time_str.tm_year = 2001 - 1900; time_str.tm_mon = 7 - 1; time_str.tm_mday = 4; time_str.tm_hour = 0; time_str.tm_min = 0; time_str.tm_sec = 1; time_str.tm_isdst = -1; if (mktime(&time_str) == -1) time_str.tm_wday = 7; printf("%s\n", wday[time_str.tm_wday]);
time
function #include <time.h>
time_t time(time_t *timer);
The time
function determines the current calendar time. The
encoding of the value is unspecified.
The time
function returns the implementation's best approximation
to the current calendar time. The value (time_t)-1 is returned if the
calendar time is not available. If timer is not a null pointer, the
return value is also assigned to the object it points to.
Except for the strftime
function, these functions return values in
one of two static objects: a broken-down time structure and an array
of char. Execution of any of the functions may overwrite the
information returned in either of these objects by any of the other
functions. The implementation shall behave as if no other library
functions call these functions.
asctime
function #include <time.h>
char *asctime(const struct tm *timeptr);
The asctime
function converts the broken-down time in the structure
pointed to by timeptr into a string in the form
Sun Sep 16 01:03:52 1973\n\0
using the equivalent of the following algorithm.
char *asctime(const struct tm *timeptr) { static const char wday_name[7][3] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" }; static const char mon_name[12][3] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" }; static char result[26];
sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n", wday_name[timeptr->tm_wday], mon_name[timeptr->tm_mon], timeptr->tm_mday, timeptr->tm_hour, timeptr->tm_min, timeptr->tm_sec, 1900 + timeptr->tm_year); return result; }
The asctime
function returns a pointer to the string.
ctime
function #include <time.h>
char *ctime(const time_t *timer);
The ctime
function converts the calendar time pointed to by timer
to local time in the form of a string. It is equivalent to
asctime(localtime(timer))
The ctime
function returns the pointer returned by the asctime
function with that broken-down time as argument.
Forward references: the localtime
function (4.12.3.4).
gmtime
function #include <time.h>
struct tm *gmtime(const time_t *timer);
The gmtime
function converts the calendar time pointed to by timer
into a broken-down time, expressed as Coordinated Universal Time
(UTC).
The gmtime
function returns a pointer to that object, or a null
pointer if UTC is not available.
localtime
function #include <time.h>
struct tm *localtime(const time_t *timer);
The localtime
function converts the calendar time pointed to by
timer into a broken-down time, expressed as local time.
The localtime
function returns a pointer to that object.
strftime
function #include <time.h>
size_t strftime(char *s, size_t maxsize,
const char *format, const struct tm *timeptr);
The strftime
function places characters into the array pointed to
by s as controlled by the string pointed to by format. The format
shall be a multibyte character sequence, beginning and ending in its
initial shift state. The format string consists of zero or more
conversion specifications and ordinary multibyte characters. A
conversion specification consists of a % character followed by a
character that determines the conversion specification's behavior.
All ordinary multibyte characters (including the terminating null
character) are copied unchanged into the array. If copying takes
place between objects that overlap, the behavior is undefined. No
more than maxsize characters are placed into the array. Each
conversion specification is replaced by appropriate characters as
described in the following list. The appropriate characters are
determined by the program's locale and by the values contained in the
structure pointed to by timeptr.
"%a" is replaced by the locale's abbreviated weekday name. "%A" is replaced by the locale's full weekday name. "%b" is replaced by the locale's abbreviated month name. "%B" is replaced by the locale's full month name. "%c" is replaced by the locale's appropriate date and time representation. "%d" is replaced by the day of the month as a decimal number (01-31). "%H" is replaced by the hour (24-hour clock) as a decimal number (00-23). "%I" is replaced by the hour (12-hour clock) as a decimal number (01-12). "%j" is replaced by the day of the year as a decimal number (001-366 ). "%m" is replaced by the month as a decimal number (01-12). "%M" is replaced by the minute as a decimal number (00-59). "%p" is replaced by the locale's equivalent of either AM or PM . "%S" is replaced by the second as a decimal number (00-60). "%U" is replaced by the week number of the year (ithe first Sunday as the first day of week 1) as a decimal number (00-53). "%w" is replaced by the weekday as a decimal number (0-6), where Sunday is 0. "%W" is replaced by the week number of the year (the first Monday as the first day of week 1) as a decimal number (00-53). "%x" is replaced by the locale's appropriate date representation. "%X" is replaced by the locale's appropriate time representation. "%y" is replaced by the year without century as a decimal number (00-99). "%Y" is replaced by the year with century as a decimal number. "%Z" is replaced by the time zone name, or by no characters if no time zone is determinable. "%%" is replaced by %.
If a conversion specification is not one of the above, the behavior is undefined.
If the total number of resulting characters including the terminating null character is not more than maxsize, the strftime function returns the number of characters placed into the array pointed to by s not including the terminating null character. Otherwise, zero is returned and the contents of the array are indeterminate.
The following names are grouped under individual headers for convenience. All external names described below are reserved no matter what headers are included by the program.
<errno.h>
Macros that begin with E and a digit or E and an upper-case letter
(followed by any combination of digits, letters and underscore) may be
added to the declarations in the <errno.h>
header.
<ctype.h>
Function names that begin with either is or to, and a lower-case
letter (followed by any combination of digits, letters and underscore)
may be added to the declarations in the <ctype.h>
header.
<locale.h>
Macros that begin with LC_ and an upper-case letter (followed by
any combination of digits, letters and underscore) may be added to the
definitions in the <locale.h>
header.
<math.h>
The names of all existing functions declared in the <math.h>
header, suffixed with f or l, are reserved respectively for
corresponding functions with float and long double arguments and
return values.
<signal.h>
Macros that begin with either SIG and an upper-case letter or SIG_
and an upper-case letter (followed by any combination of digits,
letters and underscore) may be added to the definitions in the
<signal.h>
header.
<stdio.h>
Lower-case letters may be added to the conversion specifiers in fprintf and fscanf. Other characters may be used in extensions.
<stdlib.h>
Function names that begin with str and a lower-case letter
(followed by any combination of digits, letters and underscore) may be
added to the declarations in the <stdlib.h>
header.
<string.h>
Function names that begin with str, mem, or wcs and a lower-case
letter (followed by any combination of digits, letters and underscore)
may be added to the declarations in the <string.h>
header.
(These appendices are not a part of American National Standard for Information Systems — Programming Language C, X3.???-1988.)
These appendices collect information that appears in the Standard, and are not necessarily complete.
The notation is described in the introduction to 3 (Language).
token: keyword identifier constant string-literal operator punctuator
preprocessing-token: header-name identifier pp-number character-constant string-literal operator punctuator each non-white-space character that cannot be one of the above
keyword: one of auto double int struct break else long switch case enum register typedef char extern return union const float short unsigned continue for signed void default goto sizeof volatile do if static while
identifier: nondigit identifier nondigit identifier digit
nondigit: one of _ a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
digit: one of 0 1 2 3 4 5 6 7 8 9
constant: floating-constant integer-constant enumeration-constant character-constant
floating-constant: fractional-constant exponent-partopt floating-suffixopt digit-sequence exponent-part floating-suffixopt
fractional-constant: digit-sequenceopt . digit-sequence digit-sequence .
exponent-part: e signopt digit-sequence E signopt digit-sequence
sign: one of + -
digit-sequence: digit digit-sequence digit
floating-suffix: one of f l F L
integer-constant: decimal-constant integer-suffixopt octal-constant integer-suffixopt hexadecimal-constant integer-suffixopt
decimal-constant: nonzero-digit decimal-constant digit
octal-constant: 0 octal-constant octal-digit
hexadecimal-constant: 0x hexadecimal-digit 0X hexadecimal-digit hexadecimal-constant hexadecimal-digit
nonzero-digit: one of 1 2 3 4 5 6 7 8 9
octal-digit: one of 0 1 2 3 4 5 6 7
hexadecimal-digit: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
integer-suffix: unsigned-suffix long-suffixopt long-suffix unsigned-suffixopt
unsigned-suffix: one of u U
long-suffix: one of l L
enumeration-constant: identifier
character-constant: ' c-char-sequence ' L' c-char-sequence '
c-char-sequence: c-char c-char-sequence c-char
c-char: any member of the source character set except the single-quote ', backslash \, or new-line character escape-sequence
escape-sequence: simple-escape-sequence octal-escape-sequence hexadecimal-escape-sequence
simple-escape-sequence: one of \' \" \? \\ \a \b \f \n \r \t \v
octal-escape-sequence: \ octal-digit \ octal-digit octal-digit \ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence: \x hexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit
string-literal: " s-char-sequenceopt " L" s-char-sequenceopt "
s-char-sequence: s-char s-char-sequence s-char
s-char: any member of the source character set except the double-quote ", backslash \, or new-line character escape-sequence
operator: one of [ ] ( ) . -> ++ -- & * + - ~ ! sizeof / % << >> < > <= >= == != ^ | && || ? : = *= /= %= += -= <<= >>= &= ^= |= , # ##
punctuator: one of [ ] ( ) { } * , : = ; ... #
header-name: < h-char-sequence > " q-char-sequence "
h-char-sequence: h-char h-char-sequence h-char
h-char: any member of the source character set except the new-line character and >
q-char-sequence: q-char q-char-sequence q-char
q-char: any member of the source character set except the new-line character and "
primary-expression: identifier constant string-literal ( expression )
postfix-expression: primary-expression postfix-expression [ expression ] postfix-expression ( argument-expression-listopt ) postfix-expression . identifier postfix-expression -> identifier postfix-expression ++ postfix-expression --
argument-expression-list: assignment-expression argument-expression-list , assignment-expression
unary-expression: postfix-expression ++ unary-expression -- unary-expression unary-operator cast-expression sizeof unary-expression sizeof ( type-name )
unary-operator: one of & * + - ~ !
cast-expression: unary-expression ( type-name ) cast-expression
multiplicative-expression: cast-expression multiplicative-expression * cast-expression multiplicative-expression / cast-expression multiplicative-expression % cast-expression
additive-expression: multiplicative-expression additive-expression + multiplicative-expression additive-expression - multiplicative-expression
shift-expression: additive-expression shift-expression << additive-expression shift-expression >> additive-expression
relational-expression: shift-expression relational-expression < shift-expression relational-expression > shift-expression relational-expression <= shift-expression relational-expression >= shift-expression
equality-expression: relational-expression equality-expression == relational-expression equality-expression != relational-expression
AND-expression: equality-expression AND-expression & equality-expression
exclusive-OR-expression: AND-expression exclusive-OR-expression ^ AND-expression
inclusive-OR-expression: exclusive-OR-expression inclusive-OR-expression | exclusive-OR-expression
logical-AND-expression: inclusive-OR-expression logical-AND-expression && inclusive-OR-expression
logical-OR-expression: logical-AND-expression logical-OR-expression || logical-AND-expression
conditional-expression: logical-OR-expression logical-OR-expression ? expression : conditional-expression
assignment-expression: conditional-expression unary-expression assignment-operator assignment-expression
assignment-operator: one of = *= /= %= += -= <<= >>= &= ^= |=
expression: assignment-expression expression , assignment-expression
declaration: declaration-specifiers init-declarator-listopt ;
declaration-specifiers: storage-class-specifier declaration-specifiersopt type-specifier declaration-specifiersopt type-qualifier declaration-specifiersopt
init-declarator-list: init-declarator init-declarator-list , init-declarator
init-declarator: declarator declarator = initializer
storage-class-specifier: typedef extern static auto register
type-specifier: void char short int long float double signed unsigned struct-or-union-specifier enum-specifier typedef-name
struct-or-union-specifier: struct-or-union identifieropt { struct-declaration-list } struct-or-union identifier
struct-or-union: struct union
struct-declaration-list: struct-declaration struct-declaration-list struct-declaration
struct-declaration: specifier-qualifier-list struct-declarator-list ;
specifier-qualifier-list: type-specifier specifier-qualifier-listopt type-qualifier specifier-qualifier-listopt
struct-declarator-list: struct-declarator struct-declarator-list , struct-declarator
struct-declarator: declarator declaratoropt : constant-expression
enum-specifier: enum identifieropt { enumerator-list } enum identifier
enumerator-list: enumerator enumerator-list , enumerator
enumerator: enumeration-constant enumeration-constant = constant-expression
type-qualifier: const volatile
declarator: pointeropt direct-declarator
direct-declarator: identifier ( declarator ) direct-declarator [ constant-expressionopt ] direct-declarator ( parameter-type-list ) direct-declarator ( identifier-listopt )
pointer: * type-qualifier-listopt * type-qualifier-listopt pointer
type-qualifier-list: type-qualifier type-qualifier-list type-qualifier
parameter-type-list: parameter-list parameter-list , ...
parameter-list: parameter-declaration parameter-list , parameter-declaration
parameter-declaration: declaration-specifiers declarator declaration-specifiers abstract-declaratoropt
identifier-list: identifier identifier-list , identifier
type-name: specifier-qualifier-list abstract-declaratoropt
abstract-declarator: pointer pointeropt direct-abstract-declarator
direct-abstract-declarator: ( abstract-declarator ) direct-abstract-declaratoropt [ constant-expressionopt ] direct-abstract-declaratoropt ( parameter-type-listopt )
initializer: assignment-expression { initializer-list } { initializer-list , }
initializer-list: initializer initializer-list , initializer
statement: labeled-statement compound-statement expression-statement selection-statement iteration-statement jump-statement
labeled-statement: identifier : statement case constant-expression : statement default : statement
compound-statement: { declaration-listopt statement-listopt }
declaration-list: declaration declaration-list declaration
statement-list: statement statement-list statement
expression-statement: expressionopt ;
selection-statement: if ( expression ) statement if ( expression ) statement else statement switch ( expression ) statement
iteration-statement: while ( expression ) statement do statement while ( expression ) ; for ( expressionopt ; expressionopt ; expressionopt ) statement
jump-statement: goto identifier ; continue ; break ; return expressionopt ;
group: group-part group group-part
group-part: pp-tokensopt new-line if-section control-line
if-section: if-group elif-groupsopt else-groupopt endif-line
if-group: # if constant-expression new-line groupopt # ifdef identifier new-line groupopt # ifndef identifier new-line groupopt
elif-groups: elif-group elif-groups elif-group
elif-group: # elif constant-expression new-line groupopt
else-group: # else new-line groupopt
endif-line: # endif new-line
control-line: # include pp-tokens new-line # define identifier replacement-list new-line # define identifier lparen identifier-listopt ) replacement-list new-line # undef identifier new-line # line pp-tokens new-line # error pp-tokensopt new-line # pragma pp-tokensopt new-line # new-line
lparen: the left-parenthesis character without preceding white-space
replacement-list: pp-tokensopt
pp-tokens: preprocessing-token pp-tokens preprocessing-token
new-line: the new-line character
The following are the sequence points described in 2.1.2.3.
<errno.h>
EDOM ERANGE errno
<stddef.h>
NULL offsetof( type, member-designator) ptrdiff_t size_t wchar_t
<assert.h>
NDEBUG void assert(int expression);
<ctype.h>
int isalnum(int c); int isalpha(int c); int iscntrl(int c); int isdigit(int c); int isgraph(int c); int islower(int c); int isprint(int c); int ispunct(int c); int isspace(int c); int isupper(int c); int isxdigit(int c); int tolower(int c); int toupper(int c);
<locale.h>
LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME NULL struct lconv char *setlocale(int category, const char *locale); struct lconv *localeconv(void);
<math.h>
HUGE_VAL double acos(double x); double asin(double x); double atan(double x); double atan2(double y, double x); double cos(double x); double sin(double x); double tan(double x); double cosh(double x); double sinh(double x); double tanh(double x); double exp(double x); double frexp(double value, int *exp); double ldexp(double x, int exp); double log(double x); double log10(double x); double modf(double value, double *iptr); double pow(double x, double y); double sqrt(double x); double ceil(double x); double fabs(double x); double floor(double x); double fmod(double x, double y);
<setjmp.h>
jmp_buf int setjmp(jmp_buf env); void longjmp(jmp_buf env, int val);
<signal.h>
sig_atomic_t SIG_DFL SIG_ERR SIG_IGN SIGABRT SIGFPE SIGILL SIGINT SIGSEGV SIGTERM void (*signal(int sig, void (*func)(int)))(int); int raise(int sig);
<stdarg.h>
va_list void va_start(va_list ap, parmN); type va_arg(va_list ap, type); void va_end(va_list ap);
<stdio.h>
_IOFBF _IOLBF _IONBF BUFSIZ EOF FILE FILENAME_MAX FOPEN_MAX fpos_t L_tmpnam NULL SEEK_CUR SEEK_END SEEK_SET size_t stderr stdin stdout TMP_MAX int remove(const char *filename); int rename(const char *old, const char *new); FILE *tmpfile(void); char *tmpnam(char *s); int fclose(FILE *stream); int fflush(FILE *stream); FILE *fopen(const char *filename, const char *mode); FILE *freopen(const char *filename, const char *mode, FILE *stream); void setbuf(FILE *stream, char *buf); int setvbuf(FILE *stream, char *buf, int mode, size_t size); int fprintf(FILE *stream, const char *format, ...); int fscanf(FILE *stream, const char *format, ...); int printf(const char *format, ...); int scanf(const char *format, ...); int sprintf(char *s, const char *format, ...); int sscanf(const char *s, const char *format, ...); int vfprintf(FILE *stream, const char *format, va_list arg); int vprintf(const char *format, va_list arg); int vsprintf(char *s, const char *format, va_list arg); int fgetc(FILE *stream); char *fgets(char *s, int n, FILE *stream); int fputc(int c, FILE *stream); int fputs(const char *s, FILE *stream); int getc(FILE *stream); int getchar(void); char *gets(char *s); int putc(int c, FILE *stream); int putchar(int c); int puts(const char *s); int ungetc(int c, FILE *stream); size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); int fgetpos(FILE *stream, fpos_t *pos); int fseek(FILE *stream, long int offset, int whence); int fsetpos(FILE *stream, const fpos_t *pos); long int ftell(FILE *stream); void rewind(FILE *stream); void clearerr(FILE *stream); int feof(FILE *stream); int ferror(FILE *stream); void perror(const char *s);
<stdlib.h>
EXIT_FAILURE EXIT_SUCCESS MB_CUR_MAX NULL RAND_MAX div_t ldiv_t size_t wchar_t double atof(const char *nptr); int atoi(const char *nptr); long int atol(const char *nptr); double strtod(const char *nptr, char **endptr); long int strtol(const char *nptr, char **endptr, int base); unsigned long int strtoul(const char *nptr, char **endptr, int base); int rand(void); void srand(unsigned int seed); void *calloc(size_t nmemb, size_t size); void free(void *ptr); void *malloc(size_t size); void *realloc(void *ptr, size_t size); void abort(void); int atexit(void (*func)(void)); void exit(int status); char *getenv(const char *name); int system(const char *string); void *bsearch(const void *key, const void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)); void qsort(void *base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)); int abs(int j); div_t div(int numer, int denom); long int labs(long int j); ldiv_t ldiv(long int numer, long int denom); int mblen(const char *s, size_t n); int mbtowc(wchar_t *pwc, const char *s, size_t n); int wctomb(char *s, wchar_t wchar); size_t mbstowcs(wchar_t *pwcs, const char *s, size_t n); size_t wcstombs(char *s, const wchar_t *pwcs, size_t n);
<string.h>
NULL size_t void *memcpy(void *s1, const void *s2, size_t n); void *memmove(void *s1, const void *s2, size_t n); char *strcpy(char *s1, const char *s2); char *strncpy(char *s1, const char *s2, size_t n); char *strcat(char *s1, const char *s2); char *strncat(char *s1, const char *s2, size_t n); int memcmp(const void *s1, const void *s2, size_t n); int strcmp(const char *s1, const char *s2); int strcoll(const char *s1, const char *s2); int strncmp(const char *s1, const char *s2, size_t n); size_t strxfrm(char *s1, const char *s2, size_t n); void *memchr(const void *s, int c, size_t n); char *strchr(const char *s, int c); size_t strcspn(const char *s1, const char *s2); char *strpbrk(const char *s1, const char *s2); char *strrchr(const char *s, int c); size_t strspn(const char *s1, const char *s2); char *strstr(const char *s1, const char *s2); char *strtok(char *s1, const char *s2); void *memset(void *s, int c, size_t n); char *strerror(int errnum); size_t strlen(const char *s);
<time.h>
CLK_TCK NULL clock_t time_t size_t struct tm clock_t clock(void); double difftime(time_t time1, time_t time0); time_t mktime(struct tm *timeptr); time_t time(time_t *timer); char *asctime(const struct tm *timeptr); char *ctime(const time_t *timer); struct tm *gmtime(const time_t *timer); struct tm *localtime(const time_t *timer); size_t strftime(char *s, size_t maxsize, const char *format, const struct tm *timeptr);
The contents of a header <limits.h>
are given below, in alphabetic
order. The minimum magnitudes shown shall be replaced by
implementation-defined magnitudes with the same sign. The values
shall all be constant expressions suitable for use in #if
preprocessing directives. The components are described further in
2.2.4.2.
#define CHAR_BIT 8 #define CHAR_MAX UCHAR_MAX or SCHAR_MAX #define CHAR_MIN 0 or SCHAR_MIN #define MB_LEN_MAX 1 #define INT_MAX +32767 #define INT_MIN -32767 #define LONG_MAX +2147483647 #define LONG_MIN -2147483647 #define SCHAR_MAX +127 #define SCHAR_MIN -127 #define SHRT_MAX +32767 #define SHRT_MIN -32767 #define UCHAR_MAX 255 #define UINT_MAX 65535 #define ULONG_MAX 4294967295 #define USHRT_MAX 65535
The contents of a header <float.h>
are given below, in alphabetic
order. The value of FLT_RADIX shall be a constant expression suitable
for use in #if preprocessing directives. Values that need not be
constant expressions shall be supplied for all other components. The
minimum magnitudes shown for integers and exponents shall be replaced
by implementation-defined magnitudes with the same sign. The
components are described further in 2.2.4.2.
#define DBL_DIG 10 #define DBL_EPSILON 1E-9 #define DBL_MANT_DIG #define DBL_MAX 1E+37 #define DBL_MAX_10_EXP +37 #define DBL_MAX_EXP #define DBL_MIN 1E-37 #define DBL_MIN_10_EXP -37 #define DBL_MIN_EXP #define FLT_DIG 6 #define FLT_EPSILON 1E-5 #define FLT_MANT_DIG #define FLT_MAX 1E+37 #define FLT_MAX_10_EXP +37 #define FLT_MAX_EXP #define FLT_MIN 1E-37 #define FLT_MIN_10_EXP -37 #define FLT_MIN_EXP #define FLT_RADIX 2 #define FLT_ROUNDS #define LDBL_DIG 10 #define LDBL_EPSILON 1E-9 #define LDBL_MANT_DIG #define LDBL_MAX 1E+37 #define LDBL_MAX_10_EXP +37 #define LDBL_MAX_EXP #define LDBL_MIN 1E-37 #define LDBL_MIN_10_EXP -37 #define LDBL_MIN_EXP
An implementation may generate warnings in many situations, none of which is specified as part of the Standard. The following are a few of the more common situations.
This appendix collects some information about portability that appears in the Standard.
The following are unspecified:
ungetc
function for a text stream, until all pushed-back
characters are read or discarded (4.9.7.11).
fgetpos
function on success
(4.9.9.1).
ftell
function for a text
stream on success (4.9.9.4).
qsort
function of two members
that compare as equal (4.10.5.2).
time
function
(4.12.2.3).
The behavior in the following circumstances is undefined:
setjmp
macro occurs in a context other than as
the controlling expression in a selection or iteration statement, or
in a comparison with an integral constant expression (possibly as
implied by the unary ! operator) as the controlling expression of a
selection or iteration statement, or as an expression statement
(possibly cast to void ) (4.6.1.1).
longjmp
function is invoked from a nested signal routine (4.6.2.1).
signal
function itself or refers to
any object with static storage duration other than by assigning a
value to a static storage duration variable of type volatile
sig_atomic_t (4.7.1.1).
signal
function such that it
returns the value SIG_ERR (4.7.1.1).
va_arg
macro (4.8.1.2).
va_end
macro is invoked without a corresponding invocation of
the va_start
macro (4.8.1.3).
va_start
macro before the va_end
macro is invoked
(4.8.1.3).
fflush
function points to an input stream or to
an update stream in which the most recent operation was input
(4.9.5.2).
fflush
function or a file
positioning function, or an input operation on an update stream is
followed by an output operation without an intervening call to a file
positioning function (4.9.5.3).
fprintf
function contains an h
or l with a conversion specifier other than d, i, n, o, u, x, or
X, or an L with a conversion specifier other than e, E, f, g, or
G (4.9.6.1).
fprintf
function contains a #
flag with a conversion specifier other than o, x, X, e, E, f, g,
or G (4.9.6.1).
fprintf
function contains a 0
flag with a conversion specifier other than d, i, o, u, x, X, e,
E, f, g, or G (4.9.6.1).
fprintf
function, except for the conversion specifiers
%s (for an array of character type) or %p (for a pointer to void )
(4.9.6.1).
fprintf
function produces more than 509
characters of output (4.9.6.1).
fscanf
function contains an h or
l with a conversion specifier other than d, i, n, o, u, or x, or
an L with a conversion specifier other than e, f, or g (4.9.6.2).
fprintf
function
during a previous program execution is the argument for %p conversion
by the fscanf
function (4.9.6.2).
fscanf
function cannot be
represented in the space provided, or the receiving object does not
have an appropriate type (4.9.6.2).
exit
function (4.10.4.3).
Each implementation shall document its behavior in each of the areas listed in this section. The following are implementation-defined:
mathematics
functions on domain errors
(4.5.1).
mathematics
functions set the integer expression errno
to the value of the macro ERANGE on underflow range errors (4.5.1).
signal
function (4.7.1.1).
signal
function
(4.7.1.1).
signal
function (4.7.1.1).
signal
function (4.7.1.1).
remove
function on an open file (4.9.4.1).
rename
function (4.9.4.2).
fprintf
function (4.9.6.1).
fscanf
function (4.9.6.2).
perror
function (4.9.10.4).
abort
function with regard to open and
temporary files (4.10.4.1).
exit
function if the value of the
argument is other than zero, EXIT_SUCCESS, or EXIT_FAILURE
(4.10.4.3).
getenv
function (4.10.4.4).
clock
function (4.12.2.1).
The following characteristics of a hosted environment are locale-specific:
The following extensions are widely used in many systems, but are not portable to all implementations. The inclusion of any extension that may cause a strictly conforming program to become invalid renders an implementation nonconforming. Examples of such extensions are new keywords, or library functions declared in standard headers or predefined macros with names that do not begin with an underscore.
In a hosted environment, the main
function receives a third
argument, char *envp[], that points to a null-terminated array of
pointers to char, each of which points to a string that provides
information about the environment for this execution of the process
(2.1.2.2).
Characters other than the underscore _, letters, and digits, that are not defined in the required source character set (such as the dollar sign $, or characters in national character sets) may appear in an identifier (3.1.2).
All characters in identifiers (with or without external linkage) are significant and case distinctions are observed (3.1.2).
A function identifier, or the identifier of an object the declaration of which contains the keyword extern, has file scope (3.1.2.1).
String literals are modifiable. Identical string literals shall be distinct (3.1.4).
Other arithmetic types, such as long long int, and their appropriate conversions are defined (3.2.2.1).
A pointer to an object or to void may be cast to a pointer to a function, allowing data to be invoked as a function (3.3.4). A pointer to a function may be cast to a pointer to an object or to void, allowing a function to be inspected or modified (for example, by a debugger) (3.3.4).
Types other than int, unsigned int, or signed int can be declared as bit-fields, with appropriate maximum widths (3.5.2.1).
The fortran type specifier may be used in a function declaration to indicate that function linkage suitable for FORTRAN is to be generated, or that different representations for external names are to be generated (3.5.4.3).
The asm keyword may be used to insert assembly-language code directly into the translator output. The most common implementation is via a statement of the form
asm ( character-string-literal );
(3.6).
There may be more than one external definition for the identifier of an object, with or without the explicit use of the keyword extern, If the definitions disagree, or more than one is initialized, the behavior is undefined (3.7.2).
A macro argument may consist of no preprocessing tokens (3.8.3).
Macro names that do not begin with an underscore, describing the translation and execution environments, may be defined by the implementation before translation begins (3.8.8).
Handlers for specific signals may be called with extra arguments in addition to the signal number (4.7.1.1).
Additional mappings from files to streams may be supported
(4.9.2), and additional file-opening modes may be specified by
characters appended to the mode argument of the fopen
function
(4.9.5.3).
The file position indicator is decremented by each successful call
to the ungetc
function for a text stream, except if its value was zero
before a call (4.9.7.11).
Only major references are listed. | |
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z abstract declarator, type name, 3.5.5
abstract machine, 2.1.2.3
abstract semantics, 2.1.2.3
active position, 2.2.2
addition assignment operator, +=, 3.3.16.2
addition operator, +, 3.3.6
additive expressions, 3.3.6
address operator, &, 3.3.3.2
aggregate type, 3.1.2.5
alignment, definition of, 1.6
alignment of structure members, 3.5.2.1
AND operator, bitwise, &, 3.3.10
AND operator, logical, &&, 3.3.13
argument, function, 3.3.2.2
argument, 1.6
argument promotion, default, 3.3.2.2
arithmetic conversions, usual, 3.2.1.5
arithmetic operators, unary, 3.3.3.3
arithmetic type, 3.1.2.5
array declarator, 3.5.4.2
array parameter, 3.7.1
array subscript operator, [ ], 3.3.2.1
array type, 3.1.2.5
array type conversion, 3.2.2.1
arrow operator, ->, 3.3.2.3
ASCII character set, 2.2.1.1
assignment operators, 3.3.16
automatic storage duration, 3.1.2.4
B A C D E F G H I J K L M N O P Q R S T U V W X Y Z base documents, 1.5
basic type, 3.1.2.5
binary stream, 4.9.2
bit, definition of, 1.6
bit, high-order, 1.6
bit, low-order, 1.6
bit-field structure member, 3.5.2.1
block, 3.6.2
block identifier scope, 3.1.2.1
broken-down-time type, 4.12.1
byte, definition of, 1.6
C A B C D E F G H I J K L M N O P Q R S T U V W X Y Z C program, 2.1.1.1
C Standard, definition of terms, 1.6
C Standard, organization of document, 1.4
C Standard, purpose of, 1.1
C Standard, references, 1.3
C Standard, scope, restrictions and limits, 1.2
case mapping functions, 4.3.2
cast expressions, 3.3.4
cast operator, ( ), 3.3.4
character, 1.6
character case mapping functions, 4.3.2
character display semantics, 2.2.2
character handling header, 4.3
character input/output functions, 4.9.7
character sets, 2.2.1
character testing functions, 4.3.1
character type conversion, 3.2.1.1
collating sequence, character set, 2.2.1
comma operator, ,, 3.3.17
command processor, 4.10.4.5
comment delimiters, /* */, 3.1.9
common initial sequence, 3.3.2.3
comparison functions, 4.11.4
complement operator, ~, 3.3.3.3
compliance, 1.7
composite type, 3.1.2.6
compound assignment operators, 3.3.16.2
compound statement, 3.6.2
concatenation functions, 4.11.3
conceptual models, 2.1
conditional inclusion, 3.8.1
conditional operator, ? :, 3.3.15
conforming freestanding implementation, 1.7
conforming hosted implementation, 1.7
conforming implementation, 1.7
conforming program, 1.7
constant, character, 3.1.3.4
constant, floating, 3.1.3.1
constant, integer, 3.1.3.2
constant, primary expression, 3.3.1
constant expressions, 3.4
constants, 3.1.3
constraints, definition of, 1.6
content, structure/union/enumeration, 3.5.2.3
contiguity, memory allocation, 4.10.3
conversion, arithmetic operands, 3.2.1
conversion, array, 3.2.2.1
conversion, characters and integers, 3.2.1.1
conversion, explicit, 3.2
conversion, floating and integral, 3.2.1.3
conversion, function, 3.2.2.1
conversion, implicit, 3.2
conversion, signed and unsigned integers, 3.2.1.2
conversion, void type, 3.2.2.2
conversions, 3.2
conversions, usual arithmetic, 3.2.1.5
copying functions, 4.11.2
D A B C E F G H I J K L M N O P Q R S T U V W X Y Z data streams, 4.9.2
date and time header, 4.12
decimal constant, 3.1.3.2
decimal digits, 2.2.1
decimal-point character, 4.1.1
declaration specifiers, 3.5
declarations, 3.5
declarators, 3.5.4
decrement operator, postfix, --, 3.3.2.4
decrement operator, prefix, --, 3.3.3.1
default argument promotions, 3.3.2.2
definition, 3.5
derived declarator types, 3.1.2.5
derived types, 3.1.2.5
device input/output, 2.1.2.3
diagnostics, 2.1.1.3
diagnostics, assert.h, 4.2
direct input/output functions, 4.9.8
display device, 2.2.2
division assignment operator, /=, 3.3.16.2
division operator, /, 3.3.5
documentation of implementation, 1.7
domain error, 4.5.1
dot operator, ., 3.3.2.3
double-precision arithmetic, 2.1.2.3
E A B C D F G H I J K L M N O P Q R S T U V W X Y Z element type, 3.1.2.5
ellipsis, unspecified parameters, , ..., 3.5.4.3
end-of-line indicator, 2.2.1
enumerated types, 3.1.2.5
enumeration content, 3.5.2.3
enumeration members, 3.5.2.2
enumeration specifiers, 3.5.2.2
enumeration tag, 3.5.2.3
enumerator, 3.5.2.2
environment, 2
environment functions, 4.10.4
environment list, 4.10.4.4
environmental considerations, 2.2
environmental limits, 2.2.4
equal-to operator, ==, 3.3.9
equality expressions, 3.3.9
error, domain, 4.5.1
error, range, 4.5.1
error conditions, 4.5.1
exception, 3.3
exclusive OR assignment operator, ^=, 3.3.16.2
exclusive OR operator, ^, 3.3.11
executable program, 2.1.1.1
execution environment, character sets, 2.2.1
execution environment limits, 2.2.4.2
execution environments, 2.1.2
explicit conversion, 3.2
exponent part, floating constant, 3.1.3.1
exponential functions, 4.5.4
expression, 3.3
expression, full, 3.6
expression, primary, 3.3.1
expression, unary, 3.3.3
expression statement, 3.6.3
external definitions, 3.7
external identifiers, underscore, 4.1.2
external linkage, 3.1.2.2
external name, 3.1.2
external object definitions, 3.7.2
F A B C D E G H I J K L M N O P Q R S T U V W X Y Z file, closing, 4.9.3
file, creating, 4.9.3
file, opening, 4.9.3
file access functions, 4.9.5
file name, 4.9.3
file operations, 4.9.4
file position indicator, 4.9.3
file positioning functions, 4.9.9
files, 4.9.3
floating arithmetic functions, 4.5.6
floating constants, 3.1.3.1
floating suffix, f or F, 3.1.3.1
floating types, 3.1.2.5
floating-point numbers, 3.1.2.5
formatted input/output functions, 4.9.6
forward references, definition of, 1.6
full expression, 3.6
fully buffered stream, 4.9.3
function, recursive call, 3.3.2.2
function argument, 3.3.2.2
function call, 3.3.2.2
function call, library, 4.1.6
function declarator, 3.5.4.3
function designator, 3.2.2.1
function identifier scope, 3.1.2.1
function image, 2.2.3
function prototype identifier scope, 3.1.2.1
function return, 3.6.6.4
function type, 3.1.2.5
function type conversion, 3.2.2.1
function-call operator, ( ), 3.3.2.2
future language directions, 3.9
future library directions, 4.13
G A B C D E F H I J K L M N O P Q R S T U V W X Y Z general utility library, 4.10
graphic characters, 2.2.1
greater-than operator, >, 3.3.8
greater-than-or-equal-to operator, >=, 3.3.8
H A B C D E F G I J K L M N O P Q R S T U V W X Y Z headers, 4.1.2
hexadecimal constant, 3.1.3.2
hexadecimal escape sequence, 3.1.3.4
high-order bit, 1.6
hyperbolic functions, 4.5.3
I A B C D E F G H J K L M N O P Q R S T U V W X Y Z identifier, maximum length, 3.1.2
identifier, reserved, 4.1.2
identifier linkage, 3.1.2.2
identifier list, 3.5.4
identifier name space, 3.1.2.3
identifier scope, 3.1.2.1
identifier type, 3.1.2.5
IEEE floating-point arithmetic standard, 2.2.4.2
implementation, definition of, 1.6
implementation-defined behavior, 1.6
implicit conversion, 3.2
implicit function declaration, 3.3.2.2
inclusive OR assignment operator, |=, 3.3.16.2
inclusive OR operator, |, 3.3.12
incomplete type, 3.1.2.5
increment operator, postfix, ++, 3.3.2.4
increment operator, prefix, ++, 3.3.3.1
indirection operator, *, 3.3.3.2
inequality operator, !=, 3.3.9
initializer braces, 3.5.7
input/output, device, 2.1.2.3
input/output header, 4.9
integer arithmetic functions, 4.10.6
integer character constant, 3.1.3.4
integer constants, 3.1.3.2
integer suffix, 3.1.3.2
integer type, 3.1.2.5
integral constant expression, 3.4
integral type, 3.1.2.5
integral type conversion, 3.2.1.3
internal linkage, 3.1.2.2
internal name, 3.1.2
iteration statements, 3.6.5
|
J A B C D E F G H I K L M N O P Q R S T U V W X Y Z jump statements, 3.6.6
K A B C D E F G H I J L M N O P Q R S T U V W X Y Z keywords, 3.1.1
L A B C D E F G H I J K M N O P Q R S T U V W X Y Z labeled statements, 3.6.1
language, 3
language, future directions, 3.9
leading underscore in identifiers, 4.1.2
left-shift assignment operator, <<=, 3.3.16.2
left-shift operator, <<, 3.3.7
length function, 4.11.6.3
less-than operator, <, 3.3.8
less-than-or-equal-to operator, <=, 3.3.8
letter, 4.1.1
library, future directions, 4.13
library functions, use of, 4.1.6
library terms, 4.1.1
limits, environmental, 2.2.4
limits, numerical, 2.2.4.2
limits, translation, 2.2.4.1
line buffered stream, 4.9.3
line number, 3.8.4
linkages of identifiers, 3.1.2.2
locale, definition of, 1.6
localization, 4.4
logarithmic functions, 4.5.4
logical AND operator, &&, 3.3.13
logical negation operator, !, 3.3.3.3
logical OR operator, ||, 3.3.14
logical source lines, 2.1.1.2
long double suffix, l or L, 3.1.3.1
long integer suffix, l or L, 3.1.3.2
low-order bit, 1.6
M A B C D E F G H I J K L N O P Q R S T U V W X Y Z macro function vs. definition, 4.1.6
macro name definition, 2.2.4.1
macro names, predefined, 3.8.8
macro, redefinition of, 3.8.3
macro replacement, 3.8.3
member-access operators, . and ->, 3.3.2.3
memory management functions, 4.10.3
minus operator, unary, -, 3.3.3.3
modifiable lvalue, 3.2.2.1
modulus function, 4.5.4.6
multiplication assignment operator, *=, 3.3.16.2
multiplication operator, *, 3.3.5
multiplicative expressions, 3.3.5
N A B C D E F G H I J K L M O P Q R S T U V W X Y Z name, file, 4.9.3
name spaces of identifiers, 3.1.2.3
nearest-integer functions, 4.5.6
nonlocal jumps header, 4.6
not-equal-to operator, !=, 3.3.9
null character padding of binary streams, 4.9.2
null pointer, 3.2.2.3
null pointer constant, 3.2.2.3
null preprocessing directive, 3.8.7
null statement, 3.6.3
number, floating-point, 3.1.2.5
numerical limits, 2.2.4.2
O A B C D E F G H I J K L M N P Q R S T U V W X Y Z object, definition of, 1.6
object type, 3.1.2.5
octal constant, 3.1.3.2
octal escape sequence, 3.1.3.4
operator, unary, 3.3.3
OR assignment operator, exclusive, ^=, 3.3.16.2
OR assignment operator, inclusive, |=, 3.3.16.2
OR operator, exclusive, ^, 3.3.11
OR operator, inclusive, |, 3.3.12
OR operator, logical, ||, 3.3.14
order of memory allocation, 4.10.3
order of evaluation of expression, 3.3
ordinary identifier name space, 3.1.2.3
P A B C D E F G H I J K L M N O Q R S T U V W X Y Z padding, null character, 4.9.2
parameter, ellipsis, , ..., 3.5.4.3
parameter, function, 3.3.2.2
parameter, main function, 2.1.2.2
parameter, 1.6
parameter type list, 3.5.4.3
parameters, program, 2.1.2.2
parenthesized expression, 3.3.1
physical source lines, 2.1.1.2
plus operator, unary, +, 3.3.3.3
pointer, null, 3.2.2.3
pointer declarator, 3.5.4.1
pointer operator, ->, 3.3.2.3
pointer to function returning type, 3.3.2.2
pointer type, 3.1.2.5
portability of implementations, 1.7
position indicator, file, 4.9.3
postfix decrement operator, --, 3.3.2.4
postfix expressions, 3.3.2
postfix increment operator, ++, 3.3.2.4
power functions, 4.5.5
precedence of expression operators, 3.3
precedence of syntax rules, 2.1.1.2
predefined macro names, 3.8.8
prefix decrement operator, --, 3.3.3.1
prefix increment operator, ++, 3.3.3.1
primary expressions, 3.3.1
program, conforming, 1.7
program, strictly conforming, 1.7
program diagnostics, 4.2.1
program execution, 2.1.2.3
program file, 2.1.1.1
program image, 2.1.1.2
program name, argv[0], 2.1.2.2
program parameters, 2.1.2.2
program structure, 2.1.1.1
promotions, default argument, 3.3.2.2
pseudo-random sequence functions, 4.10.2
punctuators, 3.1.6
Q A B C D E F G H I J K L M N O P R S T U V W X Y Z qualified types, 3.1.2.5
R A B C D E F G H I J K L M N O P Q S T U V W X Y Z range error, 4.5.1
recursive function call, 3.3.2.2
redefinition of macro, 3.8.3
referenced type, 3.1.2.5
relational expressions, 3.3.8
reliability of data, interrupted, 2.1.2.3
remainder assignment operator, %=, 3.3.16.2
remainder operator, %, 3.3.5
restore calling environment function, 4.6.2.1
reserved identifiers, 4.1.2
right-shift assignment operator, >>=, 3.3.16.2
right-shift operator, >>, 3.3.7
rvalue, 3.2.2.1
S A B C D E F G H I J K L M N O P Q R T U V W X Y Z save calling environment function, 4.6.1.1
scalar type, 3.1.2.5
scope of identifiers, 3.1.2.1
selection statements, 3.6.4
shift expressions, 3.3.7
simple assignment operator, =, 3.3.16.1
single-precision arithmetic, 2.1.2.3
sort function, 4.10.5.2
source character set, 2.2.1
source file inclusion, 3.8.2
source files, 2.1.1.1
source text, 2.1.1.2
standard headers, 4.1.2
statements, 3.6
static storage duration, 3.1.2.4
storage duration, 3.1.2.4
storage-class specifier, 3.5.1
stream, fully buffered, 4.9.3
stream, line buffered, 4.9.3
stream, unbuffered, 4.9.3
streams, 4.9.2
strictly conforming program, 1.7
string, 4.1.1
string conversion functions, 4.10.1
string handling header, 4.11
structure/union arrow operator, ->, 3.3.2.3
structure/union content, 3.5.2.3
structure/union dot operator, ., 3.3.2.3
structure/union member name space, 3.1.2.3
structure/union specifiers, 3.5.2.1
structure/union tag, 3.5.2.3
subtraction assignment operator, -=, 3.3.16.2
subtraction operator, -, 3.3.6
suffix, floating constant, 3.1.3.1
suffix, integer constant, 3.1.3.2
switch body, 3.6.4.2
syntactic categories, 3
syntax notation, 3
syntax rules, precedence of, 2.1.1.2
T A B C D E F G H I J K L M N O P Q R S U V W X Y Z tab characters, 2.2.1
tabs, white space, 3.1
tag, enumeration, 3.5.2.3
tag, structure/union, 3.5.2.3
tag name space, 3.1.2.3
tentative definitions, 3.7.2
text stream, 4.9.2
time components, 4.12.1
time conversion functions, 4.12.3
time manipulation functions, 4.12.2
top type, 3.1.2.5
translation environment, 2.1.1
translation limits, 2.2.4.2
translation phases, 2.1.1.2
trigonometric functions, 4.5.2
type, composite, 3.1.2.6
type, function, 3.1.2.5
type, incomplete, 3.1.2.5
type, object, 3.1.2.5
type, qualified, 3.1.2.5
type, unqualified, 3.1.2.5
type conversions, 3.2
type definitions, 3.5.6
type names, 3.5.5
type specifiers, 3.5.2
type qualifiers, 3.5.3
types, 3.1.2.5
U A B C D E F G H I J K L M N O P Q R S T V W X Y Z unary arithmetic operators, 3.3.3.3
unary expressions, 3.3.3
unary minus operator, -, 3.3.3.3
unary operators, 3.3.3
unary plus operator, +, 3.3.3.3
unbuffered stream, 4.9.3
undefined behavior, 1.6
underscore, leading, in identifiers, 4.1.2
union tag, 3.5.2.3
unqualified type, 3.1.2.5
unsigned integer suffix, u or U, 3.1.3.2
unspecified behavior, 1.6
usual arithmetic conversions, 3.2.1.5
V A B C D E F G H I J K L M N O P Q R S T U W X Y Z value part, floating constant, 3.1.3.1
variable arguments header, 4.8
visibility of identifiers, 3.1.2.1
void expression, 3.2.2.2
volatile storage, 2.1.2.3
W A B C D E F G H I J K L M N O P Q R S T U V X Y Z wide character, 3.1.3.4
wide character constant, 3.1.3.4
|
1) This Standard is designed to promote the portability of C programs among a variety of data-processing systems. It is intended for use by implementors and knowledgeable programmers, and is not a tutorial. It is accompanied by a Rationale document that explains many of the decisions of the Technical Committee that produced it.
2) Strictly conforming programs are intended to be maximally portable among conforming implementations. Conforming programs may depend upon nonportable features of a conforming implementation.
3) Implementations must behave as if these separate phases occur, even though many are typically folded together in practice.
4) As described in 3.1, the process of dividing a source file's characters into preprocessing tokens is context-dependent. For example, see the handling of < within a #include preprocessing directive.
5) The trigraph sequences enable the input of characters that are not defined in the "ISO 646-1983" Invariant Code Set, which is a subset of the seven-bit ASCII code set.
6) Implementations should avoid imposing fixed translation limits whenever possible.
8) This model precludes floating-point representations other than sign-magnitude.
9) The floating-point model in that standard sums powers of from zero, so the values of the exponent limits are one less than shown here.
10) See “future language directions” (3.9.1).
11) There is only one name space for tags even though three are possible.
12) In the case of a volatile object, the last store may not be explicit in the program.
13) A positional representation for integers that uses the binary digits 0 and 1, in which the values represented by successive bits are additive, begin with 1, and are multiplied by successive integral powers of 2, except perhaps the bit with the highest position.
14) Note that aggregate type does not include union type because an object with union type can only contain one member at a time.
15) There are three distinct combinations of qualified types.
16) Two types need not be identical to be compatible.
17) The semantics of these characters were discussed in 2.2.2.
18) See “future language directions” (3.9.2).
19) A character string literal need not be a string (see 4.1.1), because a null character may be embedded in it by a \0 escape sequence.
20) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
21) Thus comments do not nest.
22) In a two's-complement representation, there is no actual change in the bit pattern except filling the high-order bits with copies of the sign bit if the unsigned integer has greater size.
23) The remaindering operation done when a value of integral type is converted to unsigned type need not be done when a value of floating type is converted to unsigned type. Thus the range of portable values is [0, U type _MAX +1).
24) The name “lvalue” comes originally from the assignment expression E1 = E2, in which the left operand E1 must be a (modifiable) lvalue. It is perhaps better considered as representing an object “locator value.” What is sometimes called “rvalue” is in this Standard described as the “value of an expression.” An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
25) Because this conversion does not occur, the operand of the sizeof operator remains a function designator and violates the constraint in 3.3.3.4.
26) This paragraph renders undefined statement expressions such as i = ++i + 1; while allowing i = i + 1;
27) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same as the order of the major subsections of this section, highest precedence first. Thus, for example, the expressions allowed as the operands of the binary + operator (3.3.6) shall be those expressions defined in 3.3.1 through 3.3.6. The exceptions are cast expressions (3.3.4) as operands of unary operators (3.3.3), and an operand contained between any of the following pairs of operators: grouping parentheses () (3.3.1), subscripting brackets [] (3.3.2.1), function-call parentheses () (3.3.2.2), and the conditional operator ?: (3.3.15). Within each major subsection, the operators have the same precedence. Left- or right-associativity is indicated in each subsection by the syntax for the expressions discussed therein.
28) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
29) Most often, this is the result of converting an identifier that is a function designator.
30) That is, a function with external linkage and no information about its parameters that returns an int. If in fact it is not defined as having type “function returning int,” the behavior is undefined.
31) A function may change the values of its parameters, but these changes cannot affect the values of the arguments. On the other hand, it is possible to pass a pointer to an object, and the function may change the value of the object pointed to. A parameter declared to have array or function type is converted to a parameter with a pointer type as described in
32) If &E is a valid pointer expression (where & is the “address-of” operator, which generates a pointer to its operand) the expression (&E)->MOS is the same as E.MOS.
33) The “byte orders” for scalar types are invisible to isolated programs that do not indulge in type punning (for example, by assigning to one member of a union and inspecting the storage by accessing another member that is an appropriately sized array of character type), but must be accounted for when conforming to externally-imposed storage layouts.
34) It is always true that if E is a function designator or an lvalue that is a valid operand of the unary & operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of an object pointer type, the cast expression *(T)P is an lvalue that has a type compatible with that to which T points. Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an address inappropriately aligned for the type of object pointed to, or the address of an object that has automatic storage duration when execution of the block in which the object is declared and of all enclosed blocks has terminated.
35) When applied to a parameter declared to have array or function type, the sizeof operator yields the size of the pointer obtained by converting as in 3.2.2.1; see 3.7.1.
36) A cast does not yield an lvalue.
37) The mapping
functions for converting a pointer to an integer or an
integer to a pointer are intended to be consistent with the addressing
structure of the execution environment.
38) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it means (a<b)<c ; in other words, “if a is less than b compare 1 to c ; otherwise compare 0 to c .”
39) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.
40) If invalid prior pointer operations, such as accesses outside array bounds, produced undefined behavior, the effect of subsequent comparisons is undefined.
41) A conditional expression does not yield an lvalue.
42) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion (specified in 3.2.2.1) that changes lvalues to “the value of the expression” which removes any type qualifiers from the top type of the expression.
43) A comma operator does not yield an lvalue.
44) The operand of a sizeof operator is not evaluated (3.3.3.4), and thus any operator in 3.3 may be used.
45) An integral constant expression must be used to specify the size of a bit-field member of a structure, the value of an enumeration constant, the size of an array, or the value of a case constant. Further constraints that apply to the integral constant expressions used in conditional-inclusion preprocessing directives are discussed in 3.8.1.
46) Thus in the following initialization, static int i = 2 || 1 / 0; the expression is a valid integral constant expression with value one.
47) Function definitions have a different syntax, described in 3.7.1.
48) See “future language directions” (3.9.3).
49) The implementation may treat any register declaration simply as an auto declaration. However, whether or not addressable storage is actually used, the address of any part of an object declared with storage-class specifier register may not be computed, either explicitly (by use of the unary & operator as discussed in 3.3.3.2) or implicitly (by converting an array name to a pointer as discussed in 3.2.2.1). Thus the only operator that can be applied to an array declared with storage-class specifier register is sizeof.
50) The unary & (address-of) operator may not be applied to a bit-field object; thus there are no pointers to or arrays of bit-field objects.
51) An unnamed bit-field is useful for padding to conform to externally-imposed layouts.
52) Thus, the identifiers of enumeration constants in the same scope shall all be distinct from each other and from other identifiers declared in ordinary declarators.
53) A similar construction with enum does not exist and is not necessary as there can be no mutual dependencies between the declaration of an enumerated type and any other type.
54) It is not needed, for example, when a typedef name is declared to be a specifier for a structure or union, or when a pointer to or a function returning a structure or union is being declared. (See incomplete types in 3.1.2.5.) The specification shall be complete before such a function is called or defined.
55) Of course, when the declaration is of a typedef name, subsequent declarations can make use of the typedef name to declare objects having the specified structure, union, or enumerated type.
56) The implementation may place a const object that is not volatile in a read-only region of storage. Moreover, the implementation need not allocate storage for such an object if its address is never used.
57) This applies to those objects that behave as if they were defined with qualified types, even if they are never actually defined as objects in the program (such as an object at a memory-mapped input/output address).
58) A volatile declaration may be used to describe an object corresponding to a memory-mapped input/output port or an object accessed by an asynchronously interrupting function. Actions on objects so declared shall not be “optimized out” by an implementation or reordered except as permitted by the rules for evaluating expressions.
59) Both of these can only occur through the use of typedef s.
60) When several “array of” specifications are adjacent, a multi-dimensional array is declared.
61) The macros defined in the <stdarg.h>
header (4.8) may be used to
access arguments that follow an ellipsis.
62) See “future language directions” (3.9.4).
63) If both function types are “old style,” parameter types are not compared.
64) As indicated by the syntax, empty parentheses in a type name are interpreted as “function with no parameter specification,” rather than redundant parentheses around the omitted identifier.
65) Unlike in the base document, any automatic duration object may be initialized.
66) Such as assignments, and function calls which have side effects.
67) Thus specifies initialization for the loop; the controlling expression, specifies an evaluation made before each iteration, such that execution of the loop continues until the expression compares equal to 0; specifies an operation (such as incrementing) that is performed after each iteration.
68) Following the contin: label is a null statement.
69) Thus, if an identifier declared with external linkage is not used in an expression, there need be no external definition for it.
70) The intent is that the top type in a function definition cannot be inherited from a typedef: typedef int F(void); /* type F is “function of no arguments returning int ” */ F f, g; /* f and g both have type compatible with F */ F f { /*...*/ } /* WRONG: syntax/constraint error */ F g() { /*...*/ } /* WRONG: declares that g returns a function */ int f(void) { /*...*/ } /* RIGHT: f has type compatible with F */ int g() { /*...*/ } /* RIGHT: g has type compatible with F */ F *e(void) { /*...*/ } /* e returns a pointer to a function */ F *((e))(void) { /*...*/ } /* same: parentheses irrelevant */ int (*fp)(void); /* fp points to a function that has type F */ F *Fp; /* Fp points to a function that has type F */
71) See “future language directions” (3.9.5).
72) A parameter is in effect declared at the head of the compound statement that constitutes the function body, and therefore may not be redeclared in the function body (except in an enclosed block).
73) Thus preprocessing directives are commonly called “lines.” These “lines” have no other syntactic significance, as all white space is equivalent except in certain situations during preprocessing (see the # character string literal creation operator in 3.8.3.2, for example).
74) Because the controlling constant expression is evaluated during translation phase 4, all identifiers either are or are not macro names — there simply are no keywords, enumeration constants, and so on.
75) Thus the constant expression in the following #if directive and if statement is not guaranteed to evaluate to the same value in these two contexts. #if 'z' - 'a' == 25 if ('z' - 'a' == 25)
76) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive before the terminating new-line character. However, comments may appear anywhere in a source file, including within a preprocessing directive.
77) Note that adjacent string literals are not concatenated into a single string literal (see the translation phases in 2.1.1.2); thus an expansion that results in two string literals is an invalid directive.
78) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens, not sequences possibly containing identifier-like subsequences (see 2.1.1.2, translation phases), they are never scanned for macro names or parameters.
79) Thus indicating a Standard-conforming implementation.
80) The functions that make use of the decimal-point character are localeconv, fprintf, fscanf, printf, scanf, sprintf, sscanf, vfprintf, vprintf, vsprintf, atof, and strtod.
81) A header is not necessarily a source file, nor are the < and > delimited sequences in header names necessarily valid source file names.
82) The list of reserved external identifiers includes errno, setjmp, and va_end.
83) The macro errno need not be the identifier of an object. It might be a modifiable lvalue resulting from a function call (for example, *errno() ).
84) Thus, a program that uses errno for error checking should set it to zero before a library function call, then inspect it before a subsequent library function call.
85) See “future library directions” (4.13.1).
86) This means that an implementation must provide an actual function for each library function, even if it also provides a macro for that function.
87) Because external identifiers and some macro names beginning with an underscore are reserved, implementations may provide special semantics for such names. For example, the identifier _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the appropriate header could specify #define abs(x) _BUILTIN_abs(x) for a compiler whose code generator will accept it. In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine function may write #undef abs whether the implementation's header provides a macro implementation of abs or a builtin implementation. The prototype for the function, which precedes and is hidden by any macro definition, is thereby revealed also.
88) The message written might be of the form Assertion failed: file line
89) See “future library directions” (4.13.2).
90) In an implementation that uses the seven-bit ASCII character set, the printing characters are those whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).
91) See “future library directions” (4.13.3).
92) The only
functions in 4.3 whose behavior is not affected by the
current locale are isdigit and isxdigit.
93) See “future library directions” (4.13.4).
94) In an implementation that supports infinities, this allows infinity as an argument to be a domain error if the mathematical domain of the function does not include infinity.
95) These functions are useful for dealing with unusual conditions encountered in a low-level function of a program.
96) For example, by executing a return statement or because another longjmp call has caused a transfer to a setjmp invocation in a function earlier in the set of nested calls.
97) See “future library directions” (4.13.5). The names of the signal numbers reflect the following terms (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation, and termination.
98) Of course, the contents of the file name strings are subject to other system-specific constraints.
99) An implementation need not distinguish between text streams and binary streams. In such an implementation, there need be no new-line characters in a text stream nor any limit to the length of a line.
100) This is described in the Base Document as a That term is not used in this Standard to avoid confusion with a pointer to an object that has type FILE.
101) Among the reasons the implementation may cause the rename function to fail are that the file is open or that it is necessary to copy its contents to effectuate its renaming.
102) Files created using strings generated by the tmpnam
function are
temporary only in the sense that their names should not collide with
those generated by conventional naming rules for the implementation.
It is still necessary to use the remove
function to remove such files
when their use is ended, and before program termination.
103) Additional characters may follow these sequences.
104) The primary use of the freopen
function is to change the file
associated with a standard text stream ( stderr, stdin, or stdout ),
as those identifiers need not be modifiable lvalues to which the value
returned by the fopen
function may be assigned.
105) The buffer must have a lifetime at least as great as the open stream, so the stream should be closed before a buffer that has automatic storage duration is deallocated upon block exit.
106) Note that 0 is taken as a flag, not as the beginning of a field width.
107) No special provisions are made for multibyte characters.
108) See “future library directions” (4.13.6).
109) No special provisions are made for multibyte characters.
110) See “future library directions” (4.13.6).
111) As vfprintf, vsprintf, and vprintf invoke the va_arg
macro, the
value of arg after the return is indeterminate.
112) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
113) See “future library directions” (4.13.7).
114) Note that this need not be the same as the representation of floating-point zero or a null pointer constant.
115) Each function is called as many times as it was registered.
116) Notice that the key-to-member comparison an ordering on the array.
117) In a two's complement representation, the absolute value of the most negative number cannot be represented.
118) The array will not be null- or zero-terminated if the value returned is n.
119) See “future library directions” (4.13.8).
120) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will not be null-terminated.
121) Thus the maximum number of characters that end up in the array pointed to by s1 is strlen(s1)+n+1.
122) The contents of “holes” used as padding for purposes of alignment within structure objects are indeterminate, unless the contents of the entire object have been set explicitly, as by the calloc or memset function. Strings shorter than their allocated space and unions may also cause problems in comparison.
123) The range [0, 60] for tm_sec allows for the occasional leap second.
124) Thus, a positive or zero value for tm_isdst causes the mktime
function initially to presume that Daylight Saving Time, respectively,
is or is not in effect for the specified time. A negative value for
tm_isdst causes the mktime
function to attempt to determine whether
Daylight Saving Time is in effect for the specified time.