Programming languages -- C
Foreword
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ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission) form the specialized system for worldwide standardization. National bodies that are member of ISO or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international organizations, governmental and non- governmental, in liaison with ISO and IEC, also take part in the work.
#2
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
#3
In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least 75% of the national bodies casting a vote.
#4
International Standard ISO/IEC 9899 was prepared by Joint Technical Committee ISO/IEC JTC 1, ``Information Technology'', subcommittee 22, ``Programming languages, their environments and system software interfaces''. The Working Group responsible for this standard (WG14) maintains a site on the World Wide Web at http://www.dkuug.dk/JTC1/SC22/WG14/ containing additional information relevant to this standard such as a Rationale for many of the decisions made during its preparation and a log of Defect Reports and Responses.
#5
This edition replaces the previous edition, ISO/IEC 9899:1990, as amended and corrected by ISO/IEC 9899/COR1:1994, ISO/IEC 9899/COR2:1995, and ISO/IEC 9899/AMD1:1995. Major changes from the previous edition include:
-- restricted character set support in <iso646.h> (originally specified in AMD1)
-- wide-character library support in <wchar.h> and <wctype.h> (originally specified in AMD1) -- restricted pointers
-- variable-length arrays
-- flexible array members
-- complex (and imaginary) support in <complex.h>
-- type-generic math macros in <tgmath.h>
-- the long long int type and library functions
-- increased translation limits
-- remove implicit int
-- the vscanf family of functions
-- reliable integer division
-- universal character names
-- extended identifiers
-- binary floating-point literals and printf/scanf conversion specifiers
-- compound literals
-- designated initializers
-- // comments
-- extended integer types in <inttypes.h> and <stdint.h>
-- remove implicit function declaration
-- preprocessor arithmetic done in intmax_t/uintmax_t
-- mixed declarations and code
-- integer constant type rules
-- integer promotion rules
-- vararg macros
-- additional math library functions in <math.h>
-- floating-point environment access in <fenv.h>
-- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support -- trailing comma allowed in enum declaration
-- %lf conversion specifier allowed in printf
-- inline functions
-- the snprintf family of functions
-- boolean type in <stdbool.h>
-- idempotent type qualifiers
-- empty macro arguments
-- new struct type compatibility rules (tag compatibility)
-- _Prama preprocessing operator
-- standard pragmas
-- __func__ predefined identifier
-- VA_COPY macro
-- additional strftime conversion specifiers
-- LIA compatibility annex
-- deprecate ungetc at the beginning of a binary file
-- remove deprecation of aliased array parameters
#6
Annexes D and F form a normative part of this standard; annexes A, B, C, E, G, H, I, J, the bibliography, and the index are for information only. In accordance with the ISO/IEC Directives, Part 3, this foreword, the introduction, notes, footnotes, and examples are for information only. Introduction
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With the introduction of new devices and extended character sets, new features may be added to this International Standard. Subclauses in the language and library clauses warn implementors and programmers of usages which, though valid in themselves, may conflict with future additions.
Light editing:
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With the introduction of new devices and extended character sets, new features may be added to this International Standard. Subclauses in the language and library clauses warn implementors and programmers of usages THAT, though valid NOW, may conflict with future additions.
Medium editing:
#1
With the introduction of new devices and extended character sets, new features may be added to this International Standard. Subclauses in the language and library clauses warn implementors and programmers of usages that, though valid now, may conflict with future additions.
I rely on William Strunk and E. B. White, "The Elements of Style," MacMillan, 1979. That idiosyncratic and opinionated book works for me /just because/ of the idiosyncracies and opinions of White and his teacher. Some think White one of the contemporary masters of prose style in English. S&W, like K&R1/2, gains much of its weight from its slimness.
(1) "that" vs. "which" S&W p.59: "That" is the defining, or restrictive pronoun, "which" the nondefining, or non-restrictive. See Rule 3.
The lawn mower that is broken is in the garage. (Tells which one)
The lawn mower, which is broken, is in the garage. (Adds a fact about the only lawn mower in question)
The use of which for that is common in written and spoken language ("Let us now go even unto Bethlehem, and see this thing which is come to pass.") Occasionally which seems preferable to that, as in the sentence from the Bible. But it would be a convenience to all if these two pronouns were used with precision. The careful writer, watchful for small conveniences, goes which- hunting, removes the defining whiches, and by so doing improves his work.
#2
Certain features are obsolescent, which means that they may be considered for withdrawal in future revisions of this International Standard. They are retained because of their widespread use, but their use in new implementations (for implementation features) or new programs (for language [6.11] or library features [7.26]) is discouraged.
#3
This International Standard is divided into four major subdivisions:
-- the introduction and preliminary elements (clauses 1-4);
-- the characteristics of environments that translate and execute C programs (clause 5);
-- the language syntax, constraints, and semantics (clause 6);
-- the library facilities (clause 7).
#4
Examples are provided to illustrate possible forms of the constructions described. Footnotes are provided to emphasize consequences of the rules described in that subclause or elsewhere in this International Standard. References are used to refer to other related subclauses. Recommendations are provided to give advice or guidance to implementors. Annexes provide additional information and summarize the information contained in this International Standard. A bibliography lists documents that were referred to during the preparation of the standard.
#5
The language clause (clause 6) is derived from ``The C Reference Manual''.
#6
The library clause (clause 7) is based on the 1984 /usr/group Standard.
#1
This International Standard specifies the form and establishes the interpretation of programs written in the C programming language.1) It specifies
-- the representation of C programs;
-- the syntax and constraints of the C language;
-- the semantic rules for interpreting C programs;
-- the representation of input data to be processed by C programs;
-- the representation of output data produced by C programs;
-- the restrictions and limits imposed by a conforming implementation of C.
#2
This International Standard does not specify
-- the mechanism by which C programs are transformed for use by a data-processing system;
-- the mechanism by which C programs are invoked for use by a data-processing system;
-- the mechanism by which input data are transformed for use by a C program;
-- the mechanism by which output data are transformed after being produced by a C program;
-- the size or complexity of a program and its data that will exceed the capacity of any specific data- processing system or the capacity of a particular processor;
-- all minimal requirements of a data-processing system that is capable of supporting a conforming implementation.
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The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
#2
ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.
#3
ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental terms.
#4
ISO 4217:1995, Codes for the representation of currencies and funds.
#5
ISO 8601:1988, Data elements and interchange formats -- Information interchange -- Representation of dates and times.
#6
ISO/IEC 10646:1993, Information technology -- Universal Multiple-Octet Coded Character Set (UCS).
#7
IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems, second edition (previously designated IEC 559:1989).
#1
For the purposes of this International Standard, the following definitions apply. Other terms are defined where they appear in italic type or on the left side of a syntax rule. Terms explicitly defined in this International Standard are not to be presumed to refer implicitly to similar terms defined elsewhere. Terms not defined in this International Standard are to be interpreted according to ISO/IEC 2382-1.
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alignment requirement that objects of a particular type be located on storage boundaries with addresses that are particular multiples of a byte address
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argument actual argument actual parameter (deprecated) expression in the comma-separated list bounded by the parentheses in a function call expression, or a sequence of preprocessing tokens in the comma-separated list bounded by the parentheses in a function-like macro invocation
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bit unit of data storage in the execution environment large enough to hold an object that may have one of two values
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NOTE It need not be possible to express the address of each individual bit of an object.
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byte addressable unit of data storage large enough to hold any member of the basic character set of the execution environment
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NOTE 1 It is possible to express the address of each individual byte of an object uniquely.
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NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order bit.
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character bit representation that fits in a byte
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constraints restrictions, both syntactic and semantic, by which the exposition of language elements is to be interpreted
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correctly rounded result a representation in the result format that is nearest in value, subject to the effective rounding mode, to what the result would be given unlimited range and precision
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diagnostic message message belonging to an implementation-defined subset of the implementation's message output
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forward references references to later subclauses of this International Standard that contain additional information relevant to this subclause
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implementation a particular set of software, running in a particular translation environment under particular control options, that performs translation of programs for, and supports execution of functions in, a particular execution environment
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implementation-defined behavior unspecified behavior where each implementation documents how the choice is made
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EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit when a signed integer is shifted right.
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implementation limits restrictions imposed upon programs by the implementation
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locale-specific behavior behavior that depends on local conventions of nationality, culture, and language that each implementation documents
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EXAMPLE An example of locale-specific behavior is whether the islower function returns true for characters other than the 26 lowercase Latin letters.
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multibyte character sequence of one or more bytes representing a member of the extended character set of either the source or the execution environment
#2
NOTE The extended character set is a superset of the basic character set.
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object region of data storage in the execution environment, the contents of which can represent values
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NOTE When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.
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parameter formal parameter formal argument (deprecated) object declared as part of a function declaration or definition that acquires a value on entry to the function, or an identifier from the comma-separated list bounded by the parentheses immediately following the macro name in a function-like macro definition
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recommended practice specifications that are strongly recommended as being in keeping with the intent of the standard, but that may be impractical for some implementations
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undefined behavior behavior, upon use of a nonportable or erroneous program construct, of erroneous data, or of indeterminately valued objects, for which this International Standard imposes no requirements
#2
NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message).
#3
EXAMPLE An example of undefined behavior is the behavior on integer overflow.
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unspecified behavior behavior where this International Standard provides two or more possibilities and imposes no requirements on which is chosen in any instance
#2
EXAMPLE An example of unspecified behavior is the order in which the arguments to a function are evaluated.
Forward references: bitwise shift operators (6.5.7), expressions (6.5), function calls (6.5.2.2), the islower function (7.4.1.6), localization (7.11).
#1
In this International 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.
#2
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 International 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''.
#3
A program that is correct in all other aspects, operating on correct data, containing unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
#4
The implementation shall not successfully translate a preprocessing translation unit containing a #error preprocessing directive unless it is part of a group skipped by conditional inclusion.
#5
A strictly conforming program shall use only those features of the language and library specified in this International Standard.2) It shall not produce output dependent on any unspecified, undefined, or implementation- defined behavior, and shall not exceed any minimum implementation limit.
#6
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 that does not use complex types and in which the use of the features specified in the library clause (clause 7) is confined to the contents of the standard headers <float.h>, <iso646.h>, <limits.h>, <stdarg.h>, <stdbool.h>, <stddef.h>, and <stdint.h>. A conforming implementation may have extensions (including additional library functions), provided they do not alter
the behavior of any strictly conforming program.3)
#7
A conforming program is one that is acceptable to a conforming implementation.4)
#8
An implementation shall be accompanied by a document that defines all implementation-defined and locale-specific characteristics and all extensions.
Forward references: conditional inclusion (6.10.1), characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h> (7.9), sizes of integer types <limits.h> (7.10), variable arguments <stdarg.h> (7.15), boolean type and values <stdbool.h> (7.16), common definitions <stddef.h> (7.17), integer types <stdint.h> (7.18).
#1
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 International 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 this clause, only a few of many possible forward references have been noted.
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A C program need not all be translated at the same time. The text of the program is kept in units called source files, (or preprocessing files) in this International Standard. A source file together with all the headers and source files included via the preprocessing directive #include is known as a preprocessing translation unit. After preprocessing, a preprocessing translation unit 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, manipulation of objects whose identifiers have external linkage, or manipulation of data files. Translation units may be separately translated and then later linked to produce an executable program.
Forward references: conditional inclusion (6.10.1), linkages of identifiers (6.2.2), source file inclusion (6.10.2), external definitions (6.9), preprocessing directives (6.10).
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The precedence among the syntax rules of translation is specified by the following phases.5)
1. Physical source file multibyte characters are mapped to the source character set (introducing new-line characters for end-of-line indicators) if necessary.
Trigraph sequences are replaced by corresponding single-character internal representations.
2. Each instance of a backslash character (\) immediately followed by a new-line character is deleted, splicing physical source lines to form logical source lines. If, as a result, a character sequence that matches the syntax of a universal character name is produced, the behavior is undefined. Only the last backslash on any physical source line shall be eligible for being part of such a splice. A source file that is not empty shall end in a new-line character, which shall not be immediately preceded by a backslash character before any such splicing takes place.
3. The source file is decomposed into preprocessing tokens6) and sequences of white-space characters (including comments). A source file shall not end in a partial preprocessing token or in a partial comment. Each comment is replaced by one space character. New- line characters are retained. Whether each nonempty sequence of white-space characters other than new-line is retained or replaced by one space character is implementation-defined.
4. Preprocessing directives are executed, macro invocations are expanded, and _Pragma unary operator expressions are executed. If a character sequence that matches the syntax of a universal character name is produced by token concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing directive causes the named header or source file to be processed from phase 1 through phase 4, recursively. All preprocessing directives are then deleted.
5. Each source character set member and escape sequence in character constants and string literals is converted to the corresponding member of the execution character set; if there is no corresponding member, it is converted to an implementation-defined member.
6. Adjacent string literal tokens are concatenated.
7. White-space characters separating tokens are no longer significant. Each preprocessing token is converted into a token. The resulting tokens are syntactically and semantically analyzed and translated as a translation unit.
8. All external object and function references are resolved. Library components are linked to satisfy external references to functions and objects not defined in the current translation. All such translator output is collected into a program image which contains information needed for execution in its execution environment.
Forward references: universal character names (6.4.3), lexical elements (6.4), preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).
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A conforming implementation shall produce at least one diagnostic message (identified in an implementation-defined manner) if a preprocessing translation unit or translation unit contains a violation of any syntax rule or constraint, even if the behavior is also explicitly specified as undefined or implementation-defined. Diagnostic messages need not be produced in other circumstances.7)
#2
EXAMPLE An implementation shall issue a diagnostic for the translation unit:
char i; int i;
because in those cases where wording in this International Standard describes the behavior for a construct as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.
#1
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 (6.7.8).
#1
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. Any library facilities available to a freestanding program, other than the minimal set required by clause 4, are implementation-defined.
#2
The effect of program termination in a freestanding environment is implementation-defined.
#1
A hosted environment need not be provided, but shall conform to the following specifications if present.
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The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and 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[]) { /* ... */ }
or equivalent;8) or in some other implementation-defined manner.
#2
If they are declared, the parameters to the main function shall obey the following constraints:
-- The value of argc shall be nonnegative.
-- argv[argc] shall be a null pointer.
-- If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host environment prior to program startup. The intent is to supply to
the program information determined prior to program startup from elsewhere in the hosted environment. If the host environment is not capable of supplying strings with letters in both uppercase and lowercase, the implementation shall ensure that the strings are received in lowercase.
-- If the value of argc is greater than zero, the string pointed to by argv[0] represents the program name; argv[0][0] shall be the null character if the program name is not available from the host environment. If the value of argc is greater than one, the strings pointed to by argv[1] through argv[argc-1] represent the program parameters.
-- The parameters argc and argv and the strings pointed to by the argv array shall be modifiable by the program, and retain their last-stored values between program startup and program termination.
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In a hosted environment, a program may use all the functions, macros, type definitions, and objects described in the library clause (clause 7).
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If the return type of the main function is a type compatible with int, 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;9) reaching the } that terminates the main function returns a value of 0. If the return type is not compatible with int, the termination status returned to the host environment is unspecified.
Forward references: definition of terms (7.1.1), the exit function (7.20.4.3).
#1
The semantic descriptions in this International Standard describe the behavior of an abstract machine in which issues of optimization are irrelevant.
#2
Accessing a volatile object, modifying an object, modifying a file, or calling a function that does any of
those operations are all side effects,10) 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. (A summary of the sequence points is given in annex C.)
#3
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).
#4
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.
#5
An instance of each object with automatic storage duration is associated with each entry into its 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).
#6
The least requirements on a conforming implementation are:
-- At sequence points, volatile objects are stable in the sense that previous accesses are complete and subsequent accesses have not yet occurred.
-- At program termination, all data written into files shall be identical to the result that execution of the program according to the abstract semantics would have produced.
-- The input and output dynamics of interactive devices shall take place as specified in 7.19.3. The intent of these requirements is that unbuffered or line-buffered output appear as soon as possible, to ensure that prompting messages actually appear prior to a program waiting for input.
#7
What constitutes an interactive device is implementation-defined.
#8
More stringent correspondences between abstract and actual semantics may be defined by each implementation.
#9
EXAMPLE 1 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.
#10
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.
#11
EXAMPLE 2 In executing the fragment
char c1, c2; /* ... */ c1 = c1 + c2;
the ``integer promotions'' require that the abstract machine promote the value of each variable to int size and then add the two ints and truncate the sum. Provided the addition of two chars can be done without overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only produce the same result, possibly omitting the promotions.
#12
EXAMPLE 3 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).
#13
EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate semantics. Values are independent of whether they are represented in a register or in memory. For example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load is required to round to the precision of the storage type. In particular, casts and assignments are required to perform their specified conversion. For the fragment
double d1, d2; float f; d1 = f = expression; d2 = (float) expressions;
the values assigned to d1 and d2 are required to have been converted to float.
#14
EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in precision as well as range. The implementation cannot generally apply the mathematical associative rules for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real numbers are often not valid (see F.8).
double x, y, z; /* ... */ x = (x * y) * z; // not equivalent to x *= y * z; z = (x - y) + y ; // not equivalent to z = x; z = x + x * y; // not equivalent to z = x * (1.0 + y); y = x / 5.0; // not equivalent to y = x * 0.2;
#15
EXAMPLE 6 To illustrate the grouping behavior of expressions, in the following fragment
int a, b; /* ... */ a = a + 32760 + b + 5;
the expression statement behaves exactly the same as
a = (((a + 32760) + b) + 5);
due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in which overflows produce an explicit trap and in which the range of values representable by an int is [-32768, +32767], the implementation cannot rewrite this expression as
a = ((a + b) + 32765);
since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap while the original expression would not; nor can the expression be rewritten either as
a = ((a + 32765) + b);
or
a = (a + (b + 32765));
since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine in which overflow silently generates some value and where positive and negative overflows cancel, the above expression statement can be rewritten by the implementation in any of the above ways because the same result will occur.
#16
EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the following fragment
#include <stdio.h> int sum; char *p; /* ... */ sum = sum * 10 - '0' + (*p++ = getchar());
the expression statement is grouped as if it were written as
sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
but the actual increment of p can occur at any time between the previous sequence point and the next sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned value.
Forward references: compound statement, or block (6.8.2), expressions (6.5), files (7.19.3), sequence points (6.5, 6.8), the signal function (7.14), type qualifiers (6.7.3).
#1
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 subclause are locale- specific.
#2
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.
#3
Both the basic source and basic execution character sets shall have at least the following members: the 26 uppercase letters of the Latin 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 lowercase letters of the Latin 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. The representation of each member of the source and execution basic character sets shall fit in a byte. 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 International 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 an identifier, a character constant, a string literal, a header name, a comment, or a preprocessing token that is never converted to a token), the behavior is undefined.
#4
The universal character name construct provides a way to name other characters.
Forward references: universal character names (6.4.3), character constants (6.4.4.4), preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).
#1
All occurrences in a source file of the following sequences of three characters (called trigraph sequences11)) 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.
#2
EXAMPLE The following source line
printf("Eh???/n");
becomes (after replacement of the trigraph sequence ??/)
printf("Eh?\n");
#1
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:
-- The single-byte characters defined in 5.2.1 shall be present.
-- The presence, meaning, and representation of any additional members is locale-specific.
-- A multibyte character set may have a state-dependent encoding, wherein each sequence of multibyte characters begins in an initial shift state and enters other locale-specific shift states when specific multibyte characters are encountered in the sequence. While in the initial shift state, all single-byte characters retain their usual interpretation and do not alter the shift state. The interpretation for subsequent bytes in the sequence is a function of the current shift state.
-- A byte with all bits zero shall be interpreted as a null character independent of shift state.
-- A byte with all bits zero shall not occur in the second or subsequent bytes of a multibyte character.
#2
For source files, the following shall hold:
-- An identifier, comment, string literal, character constant, or header name shall begin and end in the initial shift state.
-- An identifier, comment, string literal, character constant, or header name shall consist of a sequence of valid multibyte characters.
#1
The active position is that location on a display device where the next character output by the fputc or fputwc function would appear. The intent of writing a printing character (as defined by the isprint or iswprint 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 writing is locale-specific. If the active position is at the final position of a line (if there is one), the behavior is unspecified.
#2
Alphabetic escape sequences representing nongraphic characters in the execution character set are intended to produce actions on display devices as follows:
\a (alert) Produces an audible or visible alert. The active position shall not be changed.
\b (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. \f (form feed) Moves the active position to the initial position at the start of the next logical page.
\n (new line) Moves the active position to the initial position of the next line.
\r (carriage return) Moves the active position to the initial position of the current line.
\t (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.
\v (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.
#3
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 International Standard.
Forward references: the isprint function (7.4.1.7), the fputc function (7.19.7.3), the fputwc functions (7.24.3.3), the iswprint function (7.25.2.1.7).
#1
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 compose the executable representation of a function) on a per-invocation basis.
#1
Both the translation and execution environments constrain the implementation of language translators and libraries. The following summarizes the language-related environmental limits on a conforming implementation; the library-related limits are discussed in clause 7.
#1
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:12)
-- 127 nesting levels of blocks
-- 63 nesting levels of conditional inclusion
-- 12 pointer, array, and function declarators (in any combinations) modifying an arithmetic, structure, union, or incomplete type in a declaration
-- 63 nesting levels of parenthesized declarators within a full declarator
-- 63 nesting levels of parenthesized expressions within a full expression
-- 63 significant initial characters in an internal identifier or a macro name (each universal character name or extended source character is considered a single character)
-- 31 significant initial characters in an external identifier (each universal character name specifying a character short identifier of 0000FFFF or less is considered 6 characters, each universal character name specifying a character short identifier of 00010000 or more is considered 10 characters, and each extended source character is considered the same number of characters as the corresponding universal character name, if any)
-- 4095 external identifiers in one translation unit
-- 511 identifiers with block scope declared in one block
-- 4095 macro identifiers simultaneously defined in one preprocessing translation unit
-- 127 parameters in one function definition
-- 127 arguments in one function call
-- 127 parameters in one macro definition
-- 127 arguments in one macro invocation
-- 4095 characters in a logical source line
-- 4095 characters in a character string literal or wide string literal (after concatenation)
-- 65535 bytes in an object (in a hosted environment only)
-- 15 nesting levels for #included files
-- 1023 case labels for a switch statement (excluding those for any nested switch statements)
-- 1023 members in a single structure or union
-- 1023 enumeration constants in a single enumeration
-- 63 levels of nested structure or union definitions in a single struct-declaration-list
#1
A conforming implementation shall document all the limits specified in this subclause, which are specified in the headers <limits.h> and <float.h>. Additional limits are specified in <stdint.h>.
#1
The values given below shall be replaced by constant expressions suitable for use in #if preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the following shall be replaced by expressions that have the same type as would an expression that is an object of the corresponding type converted according to the integer promotions. Their implementation-defined values shall be equal or greater in magnitude (absolute value) to those shown, with the same sign.
-- number of bits for smallest object that is not a bit- field (byte) CHAR_BIT 8
-- minimum value for an object of type signed char SCHAR_MIN -127 // -(27-1)
-- maximum value for an object of type signed char SCHAR_MAX +127 // 27-1
-- maximum value for an object of type unsigned char UCHAR_MAX 255 // 28-1
-- minimum value for an object of type char CHAR_MIN see below -- maximum value for an object of type char CHAR_MAX see below
-- maximum number of bytes in a multibyte character, for any supported locale MB_LEN_MAX 1
-- minimum value for an object of type short int SHRT_MIN -32767 // -(215-1)
-- maximum value for an object of type short int SHRT_MAX +32767 // 215-1
-- maximum value for an object of type unsigned short int USHRT_MAX 65535 // 216-1
-- minimum value for an object of type int INT_MIN -32767 // -(215-1)
-- maximum value for an object of type int INT_MAX +32767 // 215-1
-- maximum value for an object of type unsigned int UINT_MAX 65535 // 216-1
-- minimum value for an object of type long int LONG_MIN -2147483647 // -(231-1)
-- maximum value for an object of type long int LONG_MAX +2147483647 // 231-1
-- maximum value for an object of type unsigned long int ULONG_MAX 4294967295 // 232-1
-- minimum value for an object of type long long int LLONG_MIN -9223372036854775807 // -(263-1)
-- maximum value for an object of type long long int LLONG_MAX +9223372036854775807 // 263-1
-- maximum value for an object of type unsigned long long int ULLONG_MAX 18446744073709551615 // 264-1
#2
If the value of an object of type char is treated as a signed integer 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. Otherwise, the value of CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of UCHAR_MAX.13) The value UCHAR_MAX+1 shall equal 2 raised to the power
CHAR_BIT.
#1
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.14) 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 integer > 1) e exponent (an integer between a minimum emin and a maximum emax) p precision (the number of base-b digits in the significand) fk nonnegative integers less than b (the significand digits)
#2
A normalized floating-point number x (f1 > 0 if x != 0) is defined by the following model:
x=s|be|k=1fk|b-k,emin<=e<=emax
#3
Floating types may include values that are not normalized floating-point numbers, for example subnormal floating-point numbers (x!=0,e=emin,f1=0), infinities, and NaNs.15) A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates through almost every arithmetic operation without raising an exception; a signaling NaN generally raises an exception when occurring as an arithmetic operand.16)
#4
The accuracy of the floating-point operations (+, -, *, /) and of the library functions in <math.h> and <complex.h> that return floating-point results is implementation defined. The implementation may state that the accuracy is unknown.
#5
All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing directives; all floating values shall
be constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, 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_EVAL_METHOD and FLT_ROUNDS.
#6
The rounding mode for floating-point addition is characterized by the value of FLT_ROUNDS:17)
-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.
#7
The values of operations with floating operands and values subject to the usual arithmetic conversions and of floating constants are evaluated to a format whose range and precision may be greater than required by the type. The use of evaluation formats is characterized by the value of FLT_EVAL_METHOD:18)
-1 indeterminable;
0 evaluate all operations and constants just to the range and precision of the type;
1 evaluate operations and constants of type float and double to the range and precision of the double type, evaluate long double operations and constants to the range and precision of the long double type;
2 evaluate all operations and constants to the range and precision of the long double type. All other negative values for FLT_EVAL_METHOD characterize implementation-defined behavior.
#8
The values given in the following list shall be
replaced by implementation-defined constant expressions with values that are greater or equal in magnitude (absolute value) to those shown, with the same sign:
-- radix of exponent representation, b FLT_RADIX 2
-- number of base-FLT_RADIX digits in the floating-point significand, p
FLT_MANT_DIG DBL_MANT_DIG LDBL_MANT_DIG
-- number of decimal digits, n, such that any floating- point number in the widest supported floating type with pmax radix b digits can be rounded to a floating-point number with n decimal digits and back again without changpmax|log10blueif b is a power of 10
|1+pmax|log10b|otherwise
DECIMAL_DIG 10
-- number of decimal digits, q, such that any floating- point number with q decimal digits can be rounded into a floating-point number with p radix b digits and back again without change to the q decimal digits, p|log10b if b is a power of 10
|(p-1)|log10b|otherwise
FLT_DIG 6 DBL_DIG 10 LDBL_DIG 10
-- minimum negative integer such that FLT_RADIX raised to one less than that power is a normalized floating-point number, emin
FLT_MIN_EXP DBL_MIN_EXP LDBL_MIN_EXP
-- minimum negative integer such that 10 raised to that power is in the range of normalized floating-point numbers, |log10bemin-1|
FLT_MIN_10_EXP -37 DBL_MIN_10_EXP -37 LDBL_MIN_10_EXP -37
-- maximum integer such that FLT_RADIX raised to one less than that power is a representable finite floating- point number, emax
FLT_MAX_EXP DBL_MAX_EXP LDBL_MAX_EXP
-- maximum integer such that 10 raised to that power is in the range of representable finite floating-point numbers, |log10((1-b-p)|bemax)| FLT_MAX_10_EXP +37 DBL_MAX_10_EXP +37 LDBL_MAX_10_EXP +37
#9
The values given in the following list shall be replaced by implementation-defined constant expressions with values that are greater than or equal to those shown:
-- maximum representable finite floating-point number, (1-b-p)|bemax
FLT_MAX 1E+37 DBL_MAX 1E+37 LDBL_MAX 1E+37
#10
The values given in the following list shall be replaced by implementation-defined constant expressions with (positive) values that are less than or equal to those shown:
-- the difference between 1 and the least value greater than 1 that is representable in the given floating point type, b1-p
FLT_EPSILON 1E-5 DBL_EPSILON 1E-9 LDBL_EPSILON 1E-9
-- minimum normalized positive floating-point number, bemin-1
FLT_MIN 1E-37 DBL_MIN 1E-37 LDBL_MIN 1E-37
#11
EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum requirements of this International Standard, and the appropriate values in a <float.h> header for type float:
x=s|16e|k=1fk|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
#12
EXAMPLE 2 The following describes floating-point representations that also meet the requirements for single- precision and double-precision normalized numbers in IEC 60559,19) and the appropriate values in a <float.h> header for types float and double:
xf=s|2e|k=1fk|2-k,-125<=e<=+128
xd=s|2e|k=1fk|2-k,-1021<=e<=+1024
FLT_RADIX 2 DECIMAL_DIG 17 FLT_MANT_DIG 24 FLT_EPSILON 1.19209290E-07F // decimal constant FLT_EPSILON 0X1P-23F // hex constant FLT_DIG 6 FLT_MIN_EXP -125 FLT_MIN 1.17549435E-38F // decimal constant FLT_MIN 0X1P-126F // hex constant FLT_MIN_10_EXP -37 FLT_MAX_EXP +128 FLT_MAX 3.40282347E+38F // decimal constant FLT_MAX 0X1.fffffeP127F // hex constant FLT_MAX_10_EXP +38 DBL_MANT_DIG 53 DBL_EPSILON 2.2204460492503131E-16 // decimal constant DBL_EPSILON 0X1P-52 // hex constant DBL_DIG 15 DBL_MIN_EXP -1021 DBL_MIN 2.2250738585072014E-308 // decimal constant DBL_MIN 0X1P-1022 // hex constant DBL_MIN_10_EXP -307 DBL_MAX_EXP +1024 DBL_MAX 1.7976931348623157E+308 // decimal constant DBL_MAX 0X1.ffffffffffffeP1023 // hex constant DBL_MAX_10_EXP +308
If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of precision), then DECIMAL_DIG would be 21.
Forward references: conditional inclusion (6.10.1), complex arithmetic <complex.h> (7.3), mathematics <math.h> (7.12), integer types <stdint.h> (7.18).
#1
In the syntax notation used in this clause, 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 suffix ``-opt'', so that
{ expression-opt }
indicates an optional expression enclosed in braces.
#2
A summary of the language syntax is given in annex A.
#1
An identifier can denote an object; a function; a tag or a member of a structure, union, or enumeration; a typedef name; a label name; a macro name; or a macro parameter. The same identifier can denote different entities at different points in the program. 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.
#2
For each different entity that an identifier designates, the identifier is visible (i.e., can be used) only within a region of program text called its scope. Different entities designated by the same identifier either have different scopes, or are in different name spaces. 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.)
#3
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).
#4
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 end of 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 identifier designates two different entities in the same name space, the scopes might overlap. If so, the scope of one entity (the inner scope) will be a strict subset of the scope of the other entity (the outer scope). Within the inner scope, the identifier designates the entity declared in the inner scope; the entity declared in the outer scope is hidden (and not visible) within the inner scope.
#5
Unless explicitly stated otherwise, where this International Standard uses the term identifier to refer to some entity (as opposed to the syntactic construct), it refers to the entity in the relevant name space whose declaration is visible at the point the identifier occurs.
#6
Two identifiers have the same scope if and only if their scopes terminate at the same point.
#7
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 (6.8.2), declarations (6.7), enumeration specifiers (6.7.2.2), function calls (6.5.2.2), function declarators (including prototypes) (6.7.5.3), function definitions (6.9.1), the goto statement (6.8.6.1), labeled statements (6.8.1), name spaces of identifiers (6.2.3), scope of macro definitions (6.10.3.5), source file inclusion (6.10.2), tags (6.7.2.3), type specifiers (6.7.2).
#1
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.
#2
In the set of translation units and libraries that constitutes an entire program, each declaration of a particular identifier with external linkage denotes the same object or function. Within one translation unit, each declaration of an identifier with internal linkage denotes the same object or function. Each declaration of an identifier with no linkage denotes a unique entity.
#3
If the declaration of a file scope identifier for an object or a function contains the storage-class specifier static, the identifier has internal linkage.20)
#4
For an identifier declared with the storage-class specifier extern in a scope in which a prior declaration of that identifier is visible,21) if the prior declaration specifies internal or external linkage, the linkage of the identifier at the later declaration is the same as the linkage specified at the prior declaration. If no prior declaration is visible, or if the prior declaration specifies no linkage, then the identifier has external linkage.
#5
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.
#6
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; a block scope identifier for an object declared without the storage-class specifier extern.
#7
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 (6.8.2), declarations (6.7), expressions (6.5), external definitions (6.9).
#1
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:
-- label names (disambiguated by the syntax of the label declaration and use);
-- the tags of structures, unions, and enumerations (disambiguated by following any22) of the keywords struct, union, or enum);
-- the members of structures or unions; each structure or union has a separate name space for its members (disambiguated by the type of the expression used to access the member via the . or -> operator);
-- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as enumeration constants).
Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1), structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags (6.7.2.3).
#1
An object has a storage duration that determines its lifetime. There are three storage durations: static, automatic, and allocated. Allocated storage is described in 7.20.3.
#2
An object whose identifier is 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, has a constant address, and retains its last-stored value throughout the execution of the entire program.23)
#3
An object whose identifier is declared with no linkage and without the storage-class specifier static has automatic storage duration.
#4
For such an object that does not have a variable length array type, storage is guaranteed to be reserved for a new
instance of the object on each entry into the block with which it is associated; the initial value of the object is indeterminate. If an initialization is specified for the object, it is performed each time the declaration is reached in the execution of the block; otherwise, the value becomes indeterminate each time the declaration is reached. Storage for the object is no longer guaranteed to be reserved when execution of the block ends in any way. (Entering an enclosed block or calling a function suspends, but does not end, execution of the current block.)
#5
For such an object that does have a variable length array type, storage is guaranteed to be reserved for a new instance of the object each time the declaration is reached in the execution of the program. The initial value of the object is indeterminate. Storage for the object is no longer guaranteed to be reserved when the execution of the program leaves the scope of the declaration.24)
#6
If an object is referred to when storage is not reserved for it, the behavior is undefined. The value of a pointer that referred to an object whose storage is no longer reserved is indeterminate. During the time that its storage is reserved, an object has a constant address.
Forward references: compound statement, or block (6.8.2), function calls (6.5.2.2), declarators (6.7.5), array declarators (6.7.5.2), initialization (6.7.8).
#1
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).
#2
An object declared as type _Bool is large enough to store the values 0 and 1.
#3
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 5.2.1 is stored in a char object, its value is guaranteed to be positive. If any other character is stored in a char object, the resulting value is implementation-defined but shall be within the range of values that can be represented in that type.
#4
There are five standard signed integer types, designated as signed char, short int, int, long int, and long long int. (These and other types may be designated in several additional ways, as described in 6.7.2.) There may also be implementation-defined extended signed integer types.25) The standard and extended signed integer types are collectively called signed integer types.26)
#5
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>).
#6
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 type _Bool and the unsigned integer types that correspond to the standard signed integer types are the standard unsigned integer types. The unsigned integer types that correspond to the extended signed integer types are the extended unsigned integer types. The standard and extended unsigned integer types are collectively called unsigned integer types.27)
#7
The standard signed integer types and standard unsigned integer types are collectively called the standard integer types, the extended signed integer types and extended
unsigned integer types are collectively called the extended integer types.
#8
For any two types with the same signedness and different integer conversion rank (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a subrange of the values of the other type.
#9
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.28) 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 type.
#10
There are three real floating types, designated as float, double, and long double.29) 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.
#11
There are three complex types, designated as float _Complex, double _Complex, and long double _Complex.30) The real floating and complex types are collectively called the floating types.
#12
For each floating type there is a corresponding real type, which is always a real floating type. For real floating types, it is the same type. For complex types, it is the type given by deleting the keyword _Complex from the type name.
#13
Each complex type has the same representation and alignment requirements as an array type containing exactly two elements of the corresponding real type; the first element is equal to the real part, and the second element to the imaginary part, of the complex number.
#14
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.31)
#15
The three types char, signed char, and unsigned char are collectively called the character types. The implementation shall define char to have the same range, representation, and behavior as either signed char or unsigned char.32)
#16
An enumeration comprises a set of named integer constant values. Each distinct enumeration constitutes a different enumerated type.
#17
The type char, the signed and unsigned integer types, and the enumerated types are collectively called integer types. The integer and real floating types are collectively called real types.
#18
The void type comprises an empty set of values; it is an incomplete type that cannot be completed.
#19
Any number of derived types can be constructed from the object, function, and incomplete types, as follows:
-- An array type describes a contiguously allocated nonempty set of objects with a particular member object type, called the element type.33) Array types are characterized by their element type and by the number of elements in the array. An array type is said to be derived from its element type, and if its element type is T, the array type is sometimes called ``array of T''. The construction of an array type from an element type is called ``array type derivation''.
-- A structure type describes a sequentially allocated nonempty set of member objects (and, in certain circumstances, an incomplete array), each of which has
an optionally specified name and possibly distinct type.
-- A union type describes an overlapping nonempty set of member objects, each of which has an optionally specified name and possibly distinct type.
-- A function type describes a function with specified return type. A function type is characterized by its return type and the number and types of its parameters. A function type is said to be derived from its return type, and if its return type is T, the function type is sometimes called ``function returning T''. The construction of a function type from a return type is called ``function type derivation''.
-- A pointer type may be derived from a function type, an object type, or an incomplete type, called the referenced type. A pointer type describes an object whose value provides a reference to an entity of the referenced type. A pointer type derived from the referenced type T is sometimes called ``pointer to T''. The construction of a pointer type from a referenced type is called ``pointer type derivation''.
#20
These methods of constructing derived types can be applied recursively.
#21
Integer 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.34)
#22
Each arithmetic type belongs to one type domain. The real type domain comprises the real types. The complex type domain comprises the complex types.
#23
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 6.7.2.3) 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. A structure type containing a flexible array member is an incomplete type that cannot be completed.
#24
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-type, a function-type, or a pointer-type derivation to T.
#25
A type is characterized by its type category, which is either the outermost derivation of a derived type (as noted above in the construction of derived types), or the type itself if the type consists of no derived types.
#26
Any type so far mentioned is an unqualified type. Each unqualified type has several qualified versions of its type,35) corresponding to the combinations of one, two, or all three of the const, volatile, and restrict qualifiers. The qualified or unqualified versions of a type are distinct types that belong to the same type category and have the same representation and alignment requirements.28) A derived type is not qualified by the qualifiers (if any) of the type from which it is derived.
#27
A pointer to void shall have the same representation and alignment requirements as a pointer to a character type. Similarly, pointers to qualified or unqualified versions of compatible types shall have the same representation and alignment requirements.28) All pointers to structure types shall have the same representation and alignment requirements as each other. All pointers to union types shall have the same representation and alignment requirements as each other. Pointers to other types need not have the same representation or alignment requirements.
#28
EXAMPLE 1 The type designated as ``float *'' has type ``pointer to float''. Its type category is pointer, 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 -- its type is ``pointer to const-qualified float'' and is a pointer to a qualified type.
#29
EXAMPLE 2 The type designated as ``struct tag (*[5])(float)'' has type ``array of pointer to function returning struct tag''. The array has length five and the function has a single parameter of type float. Its type category is array.
Forward references: character constants (6.4.4.4), compatible type and composite type (6.2.7), declarations (6.7), tags (6.7.2.3), type qualifiers (6.7.3).
#1
The representations of all types are unspecified except as stated in this subclause.
#2
Except for bit-fields, objects are composed of contiguous sequences of one or more bytes, the number, order, and encoding of which are either explicitly specified or implementation-defined.
#3
Values stored in objects of type unsigned char shall be represented using a pure binary notation.36)
#4
Values stored in objects of any other object type consist of n|CHAR_BIT bits, where n is the size of an object of that type, in bytes. The value may be copied into an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is called the object representation of the value. Two values (other than NaNs) with the same object representation compare equal, but values that compare equal may have different object representations.
#5
Certain object representations need not represent a value of the object type. If the stored value of an object has such a representation and is accessed by an lvalue expression that does not have character type, the behavior is undefined. If such a representation is produced by a side effect that modifies all or any part of the object by an lvalue expression that does not have character type, the behavior is undefined.37) Such a representation is called a trap representation.
#6
When a value is stored in an object of structure or union type, including in a member object, the bytes of the object representation that correspond to any padding bytes take unspecified values.38) The values of padding bytes
shall not affect whether the value of such an object is a trap representation. Those bits of a structure or union object that are in the same byte as a bit-field member, but are not part of that member, shall similarly not affect whether the value of such an object is a trap representation.
#7
When a value is stored in a member of an object of union type, the bytes of the object representation that do not correspond to that member but do correspond to other members take unspecified values, but the value of the union object shall not thereby become a trap representation.
#8
Where an operator is applied to a value which has more than one object representation, which object representation is used shall not affect the value of the result. Where a value is stored in an object using a type that has more than one object representation for that value, it is unspecified which representation is used, but a trap representation shall not be generated.
#1
For unsigned integer types other than unsigned char, the bits of the object representation shall be divided into two groups: value bits and padding bits (there need not be any of the latter). If there are N value bits, each bit shall represent a different power of 2 between 1 and 2N-1, so that objects of that type shall be capable of representing values from 0 to 2N-1 using a pure binary representation; this shall be known as the value representation. The values of any padding bits are unspecified.39)
#2
For signed integer types, the bits of the object representation shall be divided into three groups: value bits, padding bits, and the sign bit. There need not be any padding bits; there shall be exactly one sign bit. Each bit that is a value bit shall have the same value as the same bit in the object representation of the corresponding unsigned type (if there are M value bits in the signed type
and N in the unsigned type, then M<=N). If the sign bit is zero, it shall not affect the resulting value. If the sign bit is one, then the value shall be modified in one of the following ways:
-- the corresponding value with sign bit 0 is negated;
-- the sign bit has the value -2N;
-- the sign bit has the value 1-2N.
#3
The values of any padding bits are unspecified.39) A valid (non-trap) object representation of a signed integer type where the sign bit is zero is a valid object representation of the corresponding unsigned type, and shall represent the same value.
#4
The precision of an integer type is the number of bits it uses to represent values, excluding any sign and padding bits. The width of an integer type is the same but including any sign bit; thus for unsigned integer types the two values are the same, while for signed integer types the width is one greater than the precision.
#1
Two types have compatible type if their types are the same. Additional rules for determining whether two types are compatible are described in 6.7.2 for type specifiers, in 6.7.3 for type qualifiers, and in 6.7.5 for declarators.40) Moreover, two structure, union, or enumerated types declared in separate translation units are compatible if their tags and members satisfy the following requirements: If one is declared with a tag, the other shall be declared with the same tag. If both are completed types, then the following additional requirements apply: there shall be a one-to-one correspondence between their members such that each pair of corresponding members are declared with compatible types, and such that if one member of a corresponding pair is declared with a name, the other member is declared with the same name. For two structures, corresponding members shall be declared in the same order. For two structures or unions, corresponding bit-fields shall have the same widths. For two enumerations, corresponding members shall have the same values.
#2
All declarations that refer to the same object or function shall have compatible type; otherwise, the behavior is undefined.
#3
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 satisfies the following conditions:
-- If one type is an array of known constant size, the composite type is an array of that size; otherwise, if one type is a variable length array, the composite type is that type.
-- If only one type is a function type with a parameter type list (a function prototype), the composite type is a function prototype with the parameter type list.
-- If both types are function types with parameter type lists, the type of each parameter in the composite parameter type list is the composite type of the corresponding parameters.
These rules apply recursively to the types from which the two types are derived.
#4
For an identifier with internal or external linkage declared in a scope in which a prior declaration of that identifier is visible,41) if the prior declaration specifies internal or external linkage, the type of the identifier at the later declaration becomes the composite type.
#5
EXAMPLE 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 (6.7.5), enumeration specifiers (6.7.2.2), structure and union specifiers (6.7.2.1), type definitions (6.7.7), type qualifiers (6.7.3), type specifiers (6.7.2).
#1
Several operators convert operand values from one type to another automatically. This subclause 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 6.3.1.8 summarizes the conversions performed by most ordinary operators; it is supplemented as required by the discussion of each operator in 6.5.
#2
Conversion of an operand value to a compatible type causes no change to the value or the representation.
Forward references: cast operators (6.5.4).
#1
Every integer type has an integer conversion rank defined as follows:
-- No two signed integer types shall have the same rank, even if they have the same representation.
-- The rank of a signed integer type shall be greater than the rank of any signed integer type with less precision.
-- The rank of long long int shall be greater than the rank of long int, which shall be greater than the rank of int, which shall be greater than the rank of short int, which shall be greater than the rank of signed char.
-- The rank of any unsigned integer type shall equal the rank of the corresponding signed integer type, if any.
-- The rank of any standard integer type shall be greater than the rank of any extended integer type with the same width.
-- The rank of char shall equal the rank of signed char and unsigned char.
-- The rank of _Bool shall be less than the rank of all other standard integer types.
-- The rank of any enumerated type shall equal the rank of the compatible integer type (see 6.7.2.2).
-- The rank of any extended signed integer type relative to another extended signed integer type with the same precision is implementation-defined, but still subject to the other rules for determining the integer conversion rank.
-- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has greater rank than T3, then T1 has greater rank than T3.
#2
The following may be used in an expression wherever an int or unsigned int may be used:
-- An object or expression with an integer type whose integer conversion rank is less than the rank of int and unsigned int.
-- A bit-field of type _Bool, int, signed int, or unsigned int.
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 integer promotions.42) All other types are unchanged by the integer promotions.
#3
The integer promotions preserve value including sign. As discussed earlier, whether a ``plain'' char is treated as signed is implementation-defined.
Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers (6.7.2.1).
#1
When any scalar value is converted to _Bool, the result is 0 if the value compares equal to 0; otherwise, the result is 1.
#1
When a value with integer type is converted to another integer type other than _Bool, if the value can be represented by the new type, it is unchanged.
#2
Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or subtracting one more than the maximum value that can be represented in the new type until the value is in the range of the new type.
#3
Otherwise, the new type is signed and the value cannot be represented in it; the result is implementation-defined.
#1
When a finite value of real floating type is converted to an integer type other than _Bool, the fractional part is discarded (i.e., the value is truncated toward zero). If the value of the integral part cannot be represented by the integer type, the behavior is undefined.43)
#2
When a value of integer type is converted to a real 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. If the value being converted is outside the range of values that can be represented, the behavior is undefined.
#1
When a float is promoted to double or long double, or a double is promoted to long double, its value is unchanged.
#2
When a double is demoted to float, a long double is demoted to double or float, or a value being represented in greater precision and range than required by its semantic type (see 6.3.1.8) is explicitly converted to its semantic type, 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 representable value, chosen in an implementation-defined manner.
#1
When a value of complex type is converted to another complex type, both the real and imaginary parts follow the conversion rules for the corresponding real types.
#1
When a value of real type is converted to a complex type, the real part of the complex result value is determined by the rules of conversion to the corresponding real type and the imaginary part of the complex result value is a positive zero or an unsigned zero.
#2
When a value of complex type is converted to a real type, the imaginary part of the complex value is discarded and the value of the real part is converted according to the conversion rules for the corresponding real type.
#1
Many operators that expect operands of arithmetic type cause conversions and yield result types in a similar way. The purpose is to determine a common real type for the operands and result. For the specified operands, each operand is converted, without change of type domain, to a type whose corresponding real type is the common real type. Unless explicitly stated otherwise, the common real type is also the corresponding real type of the result, whose type domain is the type domain of the operands if they are the same, and complex otherwise. This pattern is called the usual arithmetic conversions:
First, if the corresponding real type of either operand is long double, the other operand is converted, without change of type domain, to a type whose corresponding real type is long double.
Otherwise, if the corresponding real type of either operand is double, the other operand is converted, without change of type domain, to a type whose corresponding real type is double.
Otherwise, if the corresponding real type of either operand is float, the other operand is converted, without change of type domain, to a type whose corresponding real type is float.44)
Otherwise, the integer promotions are performed on both operands. Then the following rules are applied to the promoted operands:
If both operands have the same type, then no further conversion is needed.
Otherwise, if both operands have signed integer types or both have unsigned integer types, the operand with the type of lesser integer conversion rank is converted to the type of the operand with greater rank.
Otherwise, if the operand that has unsigned integer type has rank greater or equal to the rank of the type of the other operand, then the operand with signed integer type is converted to the type of the operand with unsigned integer type.
Otherwise, if the type of the operand with signed integer type can represent all of the values of the type of the operand with unsigned integer type, then the operand with unsigned integer type is converted to the type of the operand with signed integer type.
Otherwise, both operands are converted to the unsigned integer type corresponding to the type of the operand with signed integer type.
#2
The values of floating operands and of the results of floating expressions may be represented in greater precision and range than that required by the type; the types are not changed thereby.45)
#1
An lvalue is an expression with an object type or an incomplete type other than void;46) if an lvalue does not designate an object when it is evaluated, the behavior is undefined. 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 or element of all contained aggregates or unions) with a const-qualified type.
#2
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.
#3
Except when it is the operand of the sizeof operator or the unary & operator, or is a string literal used to initialize an array, an expression that has type ``array of type'' is converted to an expression with type ``pointer to type'' that points to the initial element of the array object and is not an lvalue. If the array object has register storage class, the behavior is undefined.
#4
A function designator is an expression that has function type. Except when it is the operand of the sizeof operator47) 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 (6.5.3.2), assignment operators (6.5.16), common definitions <stddef.h> (7.17), initialization (6.7.8), postfix increment and decrement operators (6.5.2.4), prefix increment and decrement operators (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3).
#1
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 is evaluated as a void expression, its value or designator is discarded. (A void expression is evaluated for its side effects.)
#1
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.
#2
For any qualifier q, 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.
#3
An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.48) If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a pointer to any object or function.
#4
Conversion of a null pointer to another pointer type yields a null pointer of that type. Any two null pointers shall compare equal.
#5
An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be properly aligned, and might not point to an entity of the referenced type.49)
#6
Any pointer type may be converted to an integer type. Except as previously specified, the result is implementation-defined. If the result cannot be represented in the integer type, the behavior is undefined. The result need not be in the range of values of any integer type.
#7
A pointer to an object or incomplete type may be converted to a pointer to a different object or incomplete type. If the resulting pointer is not correctly aligned50) for the pointed-to type, the behavior is undefined. Otherwise, when converted back again, the result shall compare equal to the original pointer. When a pointer to an object is converted to a pointer to a character type, the result points to the lowest addressed byte of the object.
Successive increments of the result, up to the size of the object, yield pointers to the remaining bytes of the object.
#8
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 whose type is not compatible with the pointed-to type, the behavior is undefined.
Forward references: cast operators (6.5.4), equality operators (6.5.9), simple assignment (6.5.16.1).
#1
each non-white-space character that cannot be one of the above
#2
Each preprocessing token that is converted to a token shall have the lexical form of a keyword, an identifier, a constant, a string literal, or a punctuator.
#3
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, 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, punctuators, and single non-white-space characters that do not lexically match the other preprocessing token categories.51) If a ' or a " character matches the last category, the behavior is undefined. Preprocessing tokens can be separated by white space; this consists of comments (described later), or white-space characters (space, horizontal tab, new-line, vertical tab, and form-feed), or both. As described in 6.10, 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.
#4
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. There is one exception to this rule: a header name preprocessing token is only recognized within a #include preprocessing directive, and within such a directive, a sequence of characters that could be either a header name or a string literal is recognized as the former.
#5
EXAMPLE 1 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.
#6
EXAMPLE 2 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 (6.4.4.4), comments (6.4.9), expressions (6.5), floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix increment and decrement operators (6.5.2.4), prefix increment and decrement operators (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals (6.4.5).
#1
keyword: one of
auto enum restrict unsigned
break extern return void
case float short volatile
char for signed while
const goto sizeof _Bool
continue if static _Complex
default inline struct _Imaginary
do int switch
double long typedef
else register union
#2
The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as keywords, and shall not be used otherwise.
#1
identifier identifier-nondigit
other implementation-defined characters
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
#2
An identifier is a sequence of nondigit characters (including the underscore _, the lowercase and uppercase Latin letters, and other characters) and digits, which designates one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct. There is no specific limit on the maximum length of an identifier.
#3
Each universal character name in an identifier shall designate a character whose encoding in ISO/IEC 10646 falls into one of the ranges specified in annex D.52) The initial character shall not be a universal character name designating a digit. An implementation may allow multibyte characters that are not part of the required source
character set to appear in identifiers; which characters and their correspondence to universal character names is implementation defined.
#4
When preprocessing tokens are converted to tokens during translation phase 7, if a preprocessing token could be converted to either a keyword or an identifier, it is converted to a keyword.
Implementation limits
#5
As discussed in 5.2.4.1, an implementation may limit the number of significant initial characters in an identifier; the limit for an external name (an identifier that has external linkage) may be more restrictive than that for an internal name (a macro name or an identifier that does not have external linkage). The number of significant characters in an identifier is implementation-defined.
#6
Any identifiers that differ in a significant character are different identifiers. If two identifiers differ only in nonsignificant characters, the behavior is undefined.
Forward references: universal character names (6.4.3), macro replacement (6.10.3).
#1
The identifier __func__ shall be implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration
static const char __func__[] = "function-name";
appeared, where function-name is the name of the lexically- enclosing function.53)
#2
This name is encoded as if the implicit declaration had been written in the source character set and then translated into the execution character set as indicated in translation phase 5.
#3
EXAMPLE Consider the code fragment:
#include <stdio.h> void myfunc(void) { printf("%s\n", __func__); /* ... */ }
Each time the function is called, it will print to the standard output stream:
myfunc
Forward references: function definitions (6.9.1).
#1
\u hex-quad
hexadecimal-digit hexadecimal-digit
hexadecimal-digit hexadecimal-digit
#2
A universal character name shall not specify a character short identifier in the range 00000000 through 00000020, 0000007F through 0000009F, or 0000D800 through 0000DFFF inclusive. A universal character name shall not designate a character in the required character set.
#3
Universal character names may be used in identifiers, character constants, and string literals to designate characters that are not in the required character set.
#4
The universal character name \Unnnnnnnn designates the character whose character short identifier (as specified by ISO/IEC 10646) is nnnnnnnn. Similarly, the universal character name \unnnn designates the character whose character short identifier is 0000nnnn.
#1
#2
The value of a constant shall be in the range of representable values for its type.
#3
Each constant has a type, determined by its form and value, as detailed later.
#1
decimal-constant integer-suffixopt
octal-constant integer-suffixopt
hexadecimal-constant integer-suffixopt
0
hexadecimal-prefix hexadecimal-digit
hexadecimal-constant hexadecimal-digit
hexadecimal-prefix: one of
0x 0X
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 of0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
unsigned-suffix long-suffixopt
unsigned-suffix long-long-suffix
long-suffix unsigned-suffixopt
long-long-suffix unsigned-suffixopt
unsigned-suffix: one of
u U
long-suffix: one of
l L
long-long-suffix: one of
ll LL
#2
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.
#3
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.
#4
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.
#5
The type of an integer constant is the first of the corresponding list in which its value can be represented.
|| | || | Octal or Hexadecimal Suffix || Decimal Constant | Constant -------------++-----------------------+------------------------ none ||int | int ||long int | unsigned int ||long long int | long int || | unsigned long int || | long long int || | unsigned long long int -------------++-----------------------+------------------------ u or U ||unsigned int | unsigned int ||unsigned long int | unsigned long int ||unsigned long long int | unsigned long long int -------------++-----------------------+------------------------ l or L ||long int | long int ||long long int | unsigned long int || | long long int || | unsigned long long int -------------++-----------------------+------------------------ Both u or U ||unsigned long int | unsigned long int and l or L ||unsigned long long int | unsigned long long int -------------++-----------------------+------------------------ ll or LL ||long long int | long long int || | unsigned long long int -------------++-----------------------+------------------------ Both u or U ||unsigned long long int | unsigned long long int and ll or LL || |
If an integer constant cannot be represented by any type in its list, it may have an extended integer type, if the extended integer type can represent its value. If all of the types in the list for the constant are signed, the extended integer type shall be signed. If all of the types in the list for the constant are unsigned, the extended integer type shall be unsigned. If the list contains both signed and unsigned types, the extended integer type may be signed or unsigned.
#1
fractional-constant exponent-partopt floating-suffixopt
digit-sequence exponent-part floating-suffixopt
hexadecimal-floating-constant:hexadecimal-prefix hexadecimal-fractional-constant
binary-exponent-part floating-suffixopt
hexadecimal-prefix hexadecimal-digit-sequence
binary-exponent-part floating-suffixopt
digit-sequenceopt . digit-sequence
e signopt digit-sequence
E signopt digit-sequence
sign: one of
+ -
hexadecimal-fractional-constant:
hexadecimal-digit-sequenceopt .
p signopt digit-sequence
P signopt digit-sequence
hexadecimal-digit-sequence hexadecimal-digit
floating-suffix: one of
f l F L
#2
A floating constant has a significand part that may be followed by an exponent part and a suffix that specifies its type. The components of the significand 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, E, p, or P followed by an exponent consisting of an optionally signed digit sequence. Either the whole-number part or the fraction part has to be present; for decimal floating constants, either the period or the exponent part has to be present.
#3
The significand part is interpreted as a (decimal or hexadecimal) rational number; the digit sequence in the exponent part is interpreted as a decimal integer. For decimal floating constants, the exponent indicates the power of 10 by which the significand part is to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2 by which the significand part is to be scaled. For decimal floating constants, and also for hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either the nearest representable value, or the larger or smaller representable value immediately adjacent to the nearest representable value, chosen in an implementation-defined manner. For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is correctly rounded.
#4
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.
#5
The implementation should produce a diagnostic message if a hexadecimal constant cannot be represented exactly in its evaluation format; the implementation should then proceed with the translation of the program.
#6
The translation-time conversion of floating constants should match the execution-time conversion of character strings by library functions, such as strtod, given matching inputs suitable for both conversions, the same result format, and default execution-time rounding.54)
#1
#2
An identifier declared as an enumeration constant has type int.
Forward references: enumeration specifiers (6.7.2.2).
#1
' c-char-sequence '
L' c-char-sequence '
any member of the source character set except the single-quote ', backslash \, or new-line character
simple-escape-sequence: one of
\' \" \? \\
\a \b \f \n \r \t \v
\ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence hexadecimal-digit
#2
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.
#3
The single-quote ', the double-quote ", the question- mark ?, the backslash \, and arbitrary integer values, are representable according to the following table of escape sequences: single quote ' \' double quote " \" question mark ? \? backslash \ \\ octal character \o ctal digits hexadecimal character \x hexadecimal digits
#4
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 \\.
#5
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 or wide character.
#6
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 or wide character.
#7
Each octal or hexadecimal escape sequence is the longest sequence of characters that can constitute the escape sequence.
#8
In addition, characters not in the required character set are representable by universal character names and certain nongraphic characters are representable by escape sequences consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t, and \v.55)
#9
The value of an octal or hexadecimal escape sequence shall be in the range of representable values for the type unsigned char for an integer character constant, or the unsigned type corresponding to wchar_t for a wide character constant.
#10
An integer character constant has type int. The value of an integer character constant containing a single character that maps to 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. If an integer character constant contains a single character or escape sequence, its value is the one that results when an object with type char whose value is that of the single character or escape sequence is converted to type int.
#11
A wide character constant has type wchar_t, an integer type defined in the <stddef.h> header. The value of a wide character constant containing a single multibyte character that maps to 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.
#12
EXAMPLE 1 The construction '\0' is commonly used to represent the null character.
#13
EXAMPLE 2 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 -1; if type char has the same range of values as unsigned char, the character constant '\xFF' has the value +255 .
#14
EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123' specifies an integer character constant containing only one character, since a hexadecimal escape sequence is terminated only by a non-hexadecimal character. To specify an integer character constant containing the two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal escape sequence is terminated after three octal digits. (The value of this two-character integer character constant is implementation-defined.)
#15
EXAMPLE 4 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: common definitions <stddef.h> (7.17), the mbtowc function (7.20.7.2).
#1
" s-char-sequenceopt "
L" s-char-sequenceopt "
any member of the source character set except the double-quote ", backslash \, or new-line character
#2
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.
#3
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 \".
#4
In translation phase 6, the multibyte character sequences specified by any sequence of adjacent character and wide string literal tokens are concatenated into a single multibyte character sequence. If any of the tokens are wide string literal tokens, the resulting multibyte character sequence is treated as a wide string literal; otherwise, it is treated as a character string literal.
#5
In translation phase 7, a byte or code of value zero is appended to each multibyte character sequence that results from a string literal or literals.56) The multibyte character sequence is then used to initialize an array of static storage duration and length just sufficient to contain the sequence. For character string literals, the array elements have type char, and are initialized with the individual bytes of the multibyte character sequence; for wide string literals, the array elements have type wchar_t, and are initialized with the sequence of wide characters corresponding to the multibyte character sequence, as defined by the mbstowcs function with an implementation- defined current locale. The value of a string literal containing a multibyte character or escape sequence not represented in the execution character set is implementation-defined.
#6
It is unspecified whether these arrays are distinct provided their elements have the appropriate values. If the program attempts to modify such an array, the behavior is undefined.
#7
EXAMPLE 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> (7.17).
#1
punctuator: one of
[ ] ( ) { } . ->
++ -- & * + - ~ !
/ % << >> < > <= >= == != ^ | && |
? : ; ...
= *= /= %= += -= <<= >>= &= ^= |=
, # ##
<: :> <% %> %: %:%:
#2
A punctuator is a symbol that has independent syntactic and semantic significance. Depending on context, it may specify an operation to be performed (which in turn may yield a value or a function designator, produce a side
effect, or some combination thereof) in which case it is known as an operator (other forms of operator also exist in some contexts). An operand is an entity on which an operator acts.
#3
In all aspects of the language, these six tokens
<: :> <% %> %: %:%:
behave, respectively, the same as these six tokens
[ ] { } # ##
except for their spelling.57)
Forward references: expressions (6.5), declarations (6.7), preprocessing directives (6.10), statements (6.8).
#1
< h-char-sequence >
" q-char-sequence "
any member of the source character set except the new-line character and >
any member of the source character set except the new-line character and "
#2
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 6.10.2.
#3
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.58) A header name preprocessing token is recognized only within a #include preprocessing directive.
#4
EXAMPLE 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 (6.10.2).
#1
. digit
#2
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+, E-, p+, p-, P+, or P- character sequences.
#3
Preprocessing number tokens lexically include all floating and integer constant tokens.
#4
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.
#1
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.59)
#2
Except within a character constant, a string literal, or a comment, the characters // introduce a comment that includes all multibyte characters up to, but not including, the next new-line character. The contents of such a comment are examined only to identify multibyte characters and to find the terminating new-line character.
#3
EXAMPLE 1
"a//b" // four-character string literal #include "//e" // undefined behavior // */ // comment, not syntax error f = g/**//h; // equivalent to f = g / h; //\ i(); // part of a two-line comment /\ / j(); // part of a two-line comment #define glue(x,y) x##y glue(/,/) k(); // syntax error, not comment /*//*/ l(); // equivalent to l(); m = n//**/o + p; // equivalent to m = n + p;
#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.
#2
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.60)
#3
The grouping of operators and operands is indicated by the syntax.61) Except as specified later (for the function- call (), &&, ||, ?:, and comma operators), the order of evaluation of subexpressions and the order in which side effects take place are both unspecified.
#4
Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |, collectively described as bitwise operators) are required to have operands that have integer type. These operators return values that depend on the internal representations of integers, and have implementation-defined and undefined aspects for signed types.
#5
If an exception occurs during the evaluation of an expression (that is, if the result is not mathematically defined or not in the range of representable values for its type), the behavior is undefined.
#6
The effective type of an object for an access to its stored value is the declared type of the object, if any.62) If a value is stored into an object having no declared type through an lvalue having a type that is not a character type, then the type of the lvalue becomes the effective type of the object for that access and for subsequent accesses that do not modify the stored value. If a value is copied into an object having no declared type using memcpy or memmove, or is copied as an array of character type, then the effective type of the modified object for that access and for subsequent accesses that do not modify the value is the effective type of the object from which the value is copied, if it has one. For all other accesses to an object having no declared type, the effective type of the object is simply the type of the lvalue used for the access.
#7
An object shall have its stored value accessed only by an lvalue expression that has one of the following types:63)
-- a type compatible with the effective type of the object,
-- a qualified version of a type compatible with the effective type of the object,
-- a type that is the signed or unsigned type corresponding to the effective type of the object,
-- a type that is the signed or unsigned type corresponding to a qualified version of the effective type of the object,
-- an aggregate or union type that includes one of the aforementioned types among its members (including, recursively, a member of a subaggregate or contained union), or
-- a character type.
#8
A floating expression may be contracted, that is, evaluated as though it were an atomic operation, thereby omitting rounding errors implied by the source code and the expression evaluation method.64) The FP_CONTRACT pragma in
<math.h> provides a way to disallow contracted expressions. Otherwise, whether and how expressions are contracted is implementation-defined.65)
#1
( expression )
#2
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).66)
#3
A constant is a primary expression. Its type depends on its form and value, as detailed in 6.4.4.
#4
A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
#5
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 (6.7).
#1
postfix-expr ( argument-expr-listopt )
postfix-expr ++
postfix-expr --
( type-name ) { initializer-list }
( type-name ) { initializer-list , }
argument-expr-list , assignment-expr
#1
One of the expressions shall have type ``pointer to object type'', the other expression shall have integer type, and the result has type ``type''.
#2
A postfix expression followed by an expression in square brackets [] is a subscripted designation of an element 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 element of an array object) and E2 is an integer, E1[E2] designates the E2-th element of E1 (counting from zero).
#3
Successive subscript operators designate an element of a multidimensional array object. If E is an n-dimensional array (n>=2) with dimensions i|j| ... |k, then E (used as other than an lvalue) is converted to a pointer to an (n-1)-dimensional array with dimensions j| ... |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).
#4
EXAMPLE Consider the array object defined by the declaration
int x[3][5];
Here x is a 3|5 array of ints; more precisely, x is an array of three element objects, each of which is an array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to a pointer to the initial array of five ints. 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 ints. When used in the expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j] yields an int.
Forward references: additive operators (6.5.6), address and indirection operators (6.5.3.2), array declarators (6.7.5.2).
#1
The expression that denotes the called function67) shall have type pointer to function returning void or returning an object type other than an array type.
#2
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.
#3
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.
#4
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.68)
#5
If the expression that denotes the called function has
type pointer to function returning an object type, the function call expression has the same type as that object type, and has the value determined as specified in 6.8.6.4. Otherwise, the function call has type void. If an attempt is made to modify the result of a function call or to access it after the next sequence point, the behavior is undefined.
#6
If the expression that denotes the called function has a type that does not include a prototype, the integer 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 includes a prototype, and either the prototype ends with an ellipsis (, ...) or the types of the arguments after promotion are not compatible with the types of the 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, except for the following cases:
-- one promoted type is a signed integer type, the other promoted type is the corresponding unsigned integer type, and the value is representable in both types;
-- one type is pointer to void and the other is a pointer to a character type.
#7
If the expression that denotes the called function has a type that does include a prototype, the arguments are implicitly converted, as if by assignment, to the types of the corresponding parameters, taking the type of each parameter to be the unqualified version of its declared type. 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.
#8
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.
#9
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.
#10
The order of evaluation of the function designator, the actual arguments, and subexpressions within the actual arguments is unspecified, but there is a sequence point before the actual call.
#11
Recursive function calls shall be permitted, both directly and indirectly through any chain of other functions.
#12
EXAMPLE 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 have to be completed before the function pointed to by pf[f1()] is called.
Forward references: function declarators (including prototypes) (6.7.5.3), function definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).
#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.
#2
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.
#3
A postfix expression followed by the . operator 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.
#4
A postfix expression followed by the -> operator 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.69) 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.
#5
With one exception, if the value of a member of a union object is used when the most recent store to the object was to a different member, the behavior is implementation-defined.70) 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 (see below), and if the union object currently contains one of these structures, it is permitted to inspect the common initial part of any of them anywhere that a declaration of the completed type of the union is visible. Two structures share a common initial sequence if corresponding members have compatible types (and, for bit-fields, the same widths) for a sequence of one or more initial members.
#6
EXAMPLE 1 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.
#7
EXAMPLE 2 In:
struct s { int i; const int ci; }; struct s s; const struct s cs; volatile struct s vs;
the various members have the types:
s.i int s.ci const int cs.i const int cs.ci const int vs.i volatile int vs.ci volatile const int
#8
EXAMPLE 3 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) if (sin(u.nf.doublenode) == 0.0) /* ... */
The following is not a valid fragment (because the union type is not visible within function f):
struct t1 { int m; }; struct t2 { int m; }; int f(struct t1 * p1, struct t2 * p2) { if (p1->m < 0) p2->m = -p2->m; return p1->m; } int g() { union { struct t1 s1; struct t2 s2; } u; /* ... */ return f(&u.s1, &u.s2); }
Forward references: address and indirection operators (6.5.3.2), structure and union specifiers (6.7.2.1).
#1
The operand of the postfix increment or decrement operator shall have qualified or unqualified real or pointer type and shall be a modifiable lvalue.
#2
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.
#3
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 (6.5.6), compound assignment (6.5.16.2).
#1
The type name shall specify an object type or an array of unknown size, but not a variable length array type.
#2
No initializer shall attempt to provide a value for an object not contained within the entire unnamed object specified by the compound literal.
#3
If the compound literal occurs outside the body of a function, the initializer list shall consist of constant expressions.
#4
A postfix expression that consists of a parenthesized type name followed by a brace-enclosed list of initializers is a compound literal. It provides an unnamed object whose value is given by the initializer list.71)
#5
If the type name specifies an array of unknown size, the size is determined by the initializer list as specified in 6.7.7, and the type of the compound literal is that of the completed array type. Otherwise (when the type name specifies an object type), the type of the compound literal is that specified by the type name. In either case, the
result is an lvalue.
#6
The value of the compound literal is that of an unnamed object initialized by the initializer list. If the compound literal occurs outside the body of a function, the object has static storage duration; otherwise, it has automatic storage duration associated with the enclosing block.
#7
All the semantic rules and constraints for initializer lists in 6.7.8 are applicable to compound literals.72)
#8
String literals, and compound literals with const- qualified types, need not designate distinct objects.73)
#9
EXAMPLE 1 The file scope definition
int *p = (int []){2, 4};
initializes p to point to the first element of an array of two ints, the first having the value two and the second, four. The expressions in this compound literal are required to be constant. The unnamed object has static storage duration.
#10
EXAMPLE 2 In contrast, in
void f(void) { int *p; /*...*/ p = (int [2]){*p}; /*...*/ }
p is assigned the address of the first element of an array of two ints, the first having the value previously pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The unnamed object has automatic storage duration.
#11
EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects created using compound literals can be passed to functions without depending on member order:
drawline((struct point){.x=1, .y=1}, (struct point){.x=3, .y=4});
Or, if drawline instead expected pointers to struct point:
drawline(&(struct point){.x=1, .y=1}, &(struct point){.x=3, .y=4});
#12
EXAMPLE 4 A read-only compound literal can be specified through constructions like:
(const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}
#13
EXAMPLE 5 The following three expressions have different meanings:
"/tmp/fileXXXXXX" (char []){"/tmp/fileXXXXXX"} (const char []){"/tmp/fileXXXXXX"}
The first always has static storage duration and has type array of char, but need not be modifiable; the last two have automatic storage duration when they occur within the body of a function, and the first of these two is modifiable.
#14
EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory and can even be shared. For example,
(const char []){"abc"} == "abc"
might yield 1 if the literals' storage is shared.
#15
EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly linked object. For example, there is no way to write a self- referential compound literal that could be used as the function argument in place of the named object endless_zeros below:
struct int_list { int car; struct int_list *cdr; }; struct int_list endless_zeros = {0, &endless_zeros}; eval(endless_zeros);
#16
EXAMPLE 8 Each compound literal creates only a single object in a given scope: struct s { int i; };
int f (void) { struct s *p = 0, *q; int j = 0; again: q = p, p = &((struct s){ j++ }); if (j < 2) goto again; return p == q && q->i == 1; }
The function f() always returns the value 1.
#17
Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would be pointing to an object which is no longer guaranteed to exist, which would result in undefined behavior.
#1
++ unary-expr
-- unary-expr
sizeof unary-expr
sizeof ( type-name )
unary-operator: one of
& * + - ~ !
#1
The operand of the prefix increment or decrement operator shall have qualified or unqualified real or pointer type and shall be a modifiable lvalue.
#2
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.
#3
The prefix -- operator is analogous to the prefix ++ operator, except that the value of the operand is decremented.
Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
#1
The operand of the unary & operator shall be either a function designator, the result of a [] or unary * operator, or an lvalue that designates an object that is not a bit- field and is not declared with the register storage-class specifier.
#2
The operand of the unary * operator shall have pointer type.
#3
The unary & operator returns the address of its operand. If the operand has type ``type'', the result has type ``pointer to type''. If the operand is the result of a unary * operator, neither that operator nor the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor the unary * that is implied by the [] is evaluated and the result is as if the & operator were removed and the [] operator were changed to a + operator. Otherwise, the result is a pointer to the object or function designated by its operand.
#4
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.74)
Forward references: storage-class specifiers (6.7.1), structure and union specifiers (6.7.2.1).
#1
The operand of the unary + or - operator shall have arithmetic type; of the ~ operator, integer type; of the ! operator, scalar type.
#2
The result of the unary + operator is the value of its (promoted) operand. The integer promotions are performed on the operand, and the result has the promoted type.
#3
The result of the unary - operator is the negative of its (promoted) operand. The integer promotions are performed on the operand, and the result has the promoted type.
#4
The result of the ~ operator is the bitwise complement of its (promoted) 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 integer promotions are performed on the operand, and the result has the promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent to the maximum value representable in that type minus E.
#5
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: characteristics of floating types <float.h> (7.7), sizes of integer types <limits.h> (7.10).
#1
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 expression that designates a bit-field member.
#2
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. The result is an integer. If the type of the operand is a variable length array type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an integer constant.
#3
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.75) 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.
#4
The value of the result is implementation-defined, and its type (an unsigned integer type) is size_t, defined in the <stddef.h> header.
#5
EXAMPLE 1 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(size_t); 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.
#6
EXAMPLE 2 Another use of the sizeof operator is to compute the number of elements in an array:
sizeof array / sizeof array[0]
#7
EXAMPLE 3 In this example, the size of a variable- length array is computed and returned from a function:
size_t fsize3 (int n) { char b[n+3]; // Variable length array. return sizeof b; // Execution time sizeof. } int main() { size_t size; size = fsize3(10); // fsize3 returns 13. return 0; }
Forward references: common definitions <stddef.h> (7.17), declarations (6.7), structure and union specifiers (6.7.2.1), type names (6.7.6), array declarators (6.7.5.2).
#1
#2
Unless the type name specifies a void type, the type name shall specify qualified or unqualified scalar type and the operand shall have scalar type.
#3
Conversions that involve pointers, other than where permitted by the constraints of 6.5.16.1, shall be specified by means of an explicit cast.
#4
Preceding an expression by a parenthesized type name converts the value of the expression to the named type. This construction is called a cast.76) A cast that specifies no conversion has no effect on the type or value of an expression.77)
Forward references: equality operators (6.5.9), function declarators (including prototypes) (6.7.5.3), simple assignment (6.5.16.1), type names (6.7.6).
#1
multiplicative-expr * cast-expr
multiplicative-expr / cast-expr
multiplicative-expr % cast-expr
#2
Each of the operands shall have arithmetic type. The operands of the % operator shall have integer type.
#3
The usual arithmetic conversions are performed on the operands.
#4
The result of the binary * operator is the product of the operands.
#5
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.
#6
When integers are divided, the result of the / operator is the algebraic quotient with any fractional part discarded.78) If the quotient a/b is representable, the expression (a/b)*b + a%b shall equal a.
#1
additive-expr + multiplicative-expr
additive-expr - multiplicative-expr
#2
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 integer type. (Incrementing is equivalent to adding 1.)
#3
For subtraction, one of the following shall hold:
-- both operands have arithmetic type;
-- both operands are pointers to qualified or unqualified versions of compatible object types; or
-- the left operand is a pointer to an object type and the right operand has integer type.
(Decrementing is equivalent to subtracting 1.)
#4
If both operands have arithmetic type, the usual arithmetic conversions are performed on them.
#5
The result of the binary + operator is the sum of the operands.
#6
The result of the binary - operator is the difference resulting from the subtraction of the second operand from the first.
#7
For the purposes of these operators, a pointer to a nonarray object behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.
#8
When an expression that has integer type is added to or subtracted from a pointer, the result has the type of the pointer operand. If the pointer operand points to an element of an array object, and the array is large enough, the result points to an element offset from the original element such that the difference of the subscripts of the resulting and original array elements equals the integer expression. In other words, if the expression P points to the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of the array object, provided they exist. Moreover, if the expression P points to the last element of an array object, the expression (P)+1 points one past the last element of the array object, and if the expression Q points one past the last element of an array object, the expression (Q)-1 points to the last element of the array object. If both the pointer operand and the result point to elements of the same array object, or one past the last element of the array object, the evaluation shall not produce an overflow; otherwise, the behavior is undefined. If the result points one past the last element of the array object, it shall not be used as the operand of a unary * operator that is evaluated.
#9
When two pointers are subtracted, both shall point to elements of the same array object, or one past the last element of the array object; the result is the difference of the subscripts of the two array elements. The size of the result is implementation-defined, and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header. If the result is not representable in an object of that type, the behavior is undefined. In other words, if the expressions P and Q point to, respectively, the i-th and j- th elements of an array object, the expression (P)-(Q) has the value i-j provided the value fits in an object of type ptrdiff_t. Moreover, if the expression P points either to an element of an array object or one past the last element of an array object, and the expression Q points to the last element of the same array object, the expression ((Q)+1)-(P) has the same value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the expression P points one past the last element of the array object, even though the expression (Q)+1 does not point to an element of the array object.79)
#10
EXAMPLE Pointer arithmetic is well defined with pointers to variable length array types.
{ int n = 4, m = 3; int a[n][m]; int (*p)[m] = a; // p == &a[0] p += 1; // p == &a[1] (*p)[2] = 99; // a[1][2] == 99 n = p - a; // n == 1 }
#11
If array a in the above example were declared to be an array of known constant size, and pointer p were declared to be a pointer to an array of the same known constant size (pointing to a), the results would be the same.
Forward references: array declarators (6.7.5.2), common definitions <stddef.h> (7.17).
#1
#2
Each of the operands shall have integer type.
#3
The integer 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 of the promoted left operand, the behavior is undefined.
#4
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|2E2, reduced modulo one more than the maximum value representable in the result type. If E1 has a signed type and nonnegative value, and E1|2E2 is representable in the result type, then that is the resulting value; otherwise, the behavior is undefined.
#5
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.
#1
#2
One of the following shall hold:
-- both operands have real type;
-- both operands are pointers to qualified or unqualified versions of compatible object types; or
-- both operands are pointers to qualified or unqualified versions of compatible incomplete types.
#3
If both of the operands have arithmetic type, the usual arithmetic conversions are performed.
#4
For the purposes of these operators, a pointer to a nonarray object behaves the same as a pointer to the first element of an array of length one with the type of the object as its element type.
#5
When two pointers are compared, the result depends on the relative locations in the address space of the objects pointed to. If two pointers to object or incomplete types both point to the same object, or both point one past the last element of the same array object, they compare equal. If the objects pointed to are members of the same aggregate object, pointers to structure members declared later compare greater than pointers to members declared earlier in the structure, and pointers to array elements with larger subscript values compare greater 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 expression P points to an element of an array object and the expression Q points to the last element of the same array object, the pointer expression Q+1 compares greater than P. In all other cases, the behavior is undefined.
#6
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.80) The result has type int.
#1
equality-expr == relational-expr
equality-expr != relational-expr
#2
One of the following shall hold:
-- both operands have arithmetic type;
-- both operands are pointers to qualified or unqualified versions of compatible types;
-- one operand is a pointer to an object or incomplete type and the other is a pointer to a qualified or unqualified version of void; or
-- one operand is a pointer and the other is a null pointer constant.
#3
The == (equal to) and != (not equal to) operators are analogous to the relational operators except for their lower precedence.81) Each of the operators yields 1 if the specified relation is true and 0 if it is false. The result has type int. For any pair of operands, exactly one of the relations is true.
#4
If both of the operands have arithmetic type, the usual
arithmetic conversions are performed. Values of complex types are equal if and only if both their real parts are equal and also their imaginary parts are equal. Any two values of arithmetic types from different type domains are equal if and only if the results of their conversions to the (complex) result type determined by the usual arithmetic conversions are equal.
#5
Otherwise, at least one operand is a pointer. If one operand is a null pointer constant, it is converted to the type of the other operand. If one operand is a pointer to an object or incomplete type and the other is a pointer to a qualified or unqualified version of void, the former is converted to the type of the latter.
#6
Two pointers compare equal if and only if both are null pointers, both are pointers to the same object (including a pointer to an object and a subobject at its beginning) or function, both are pointers to one past the last element of the same array object, or one is a pointer to one past the end of one array object and the other is a pointer to the start of a different array object that happens to immediately follow the first array object in the address space.82)
#1
#2
Each of the operands shall have integer type.
#3
The usual arithmetic conversions are performed on the operands.
#4
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).
#1
#2
Each of the operands shall have integer type.
#3
The usual arithmetic conversions are performed on the operands.
#4
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).
#1
inclusive-OR-expr | exclusive-OR-expr
#2
Each of the operands shall have integer type.
#3
The usual arithmetic conversions are performed on the operands.
#4
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).
#1
logical-AND-expr && inclusive-OR-expr
#2
Each of the operands shall have scalar type.
#3
The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it yields 0. The result has type int.
#4
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.
#1
logical-OR-expr || logical-AND-expr
#2
Each of the operands shall have scalar type.
#3
The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it yields 0. The result has type int.
#4
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.
#1
logical-OR-expr ? expression : conditional-expr
#2
The first operand shall have scalar type.
#3
One of the following shall hold for the second and third operands:
-- both operands have arithmetic type;
-- both operands have compatible structure or union types;
-- both operands have void type;
-- both operands are pointers to qualified or unqualified versions of compatible types;
-- one operand is a pointer and the other is a null pointer constant; or
-- one operand is a pointer to an object or incomplete type and the other is a pointer to a qualified or unqualified version of void.
#4
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 result is the value of the second or third operand (whichever is evaluated), converted to the type described below.83) If an attempt is made to modify the result of a conditional operator or to access it after the next sequence point, the behavior is undefined.
#5
If both the second and third operands have arithmetic type, the result type that would be determined by the usual arithmetic conversions, were they applied to those two operands, is the type of the result. 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.
#6
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 to differently qualified versions of compatible types, the result type is a pointer to an appropriately qualified version of 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 result type is a pointer to an appropriately qualified version of void.
#7
EXAMPLE The common type that results when the second and third operands are pointers is determined in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two pointers have compatible types.
#8
Given the declarations
const void *c_vp; void *vp; const int *c_ip; volatile int *v_ip; int *ip; const char *c_cp;
the third column in the following table is the common type that is the result of a conditional expression in which the first two columns are the second and third operands (in either order):
c_vp c_ip const void * v_ip 0 volatile int * c_ip v_ip const volatile int * vp c_cp const void * ip c_ip const int * vp ip void *
#1
unary-expr assignment-operator assignment-expr
assignment-operator: one of
= *= /= %= += -= <<= >>= &= ^= |=
#2
An assignment operator shall have a modifiable lvalue as its left operand.
#3
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.
#4
The order of evaluation of the operands is unspecified. If an attempt is made to modify the result of an assignment operator or to access it after the next sequence point, the behavior is undefined.
#1
One of the following shall hold:84)
-- the left operand has qualified or unqualified arithmetic type and the right has arithmetic type;
-- the left operand has a qualified or unqualified version of a structure or union type compatible with the type of the right;
-- both operands are pointers to qualified or unqualified versions of compatible types, and the type pointed to by the left has all the qualifiers of the type pointed to by the right;
-- one operand is a pointer to an object or incomplete type and the other is a pointer to a qualified or unqualified version of void, and the type pointed to by the left has all the qualifiers of the type pointed to by the right; or
-- the left operand is a pointer and the right is a null pointer constant.
-- the left operand has type _Bool and the right is a pointer.
#2
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.
#3
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.
#4
EXAMPLE 1 In the program fragment
int f(void); char c; /* ... */ if ((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.
#5
EXAMPLE 2 In the fragment:
char c; int i; long l; l = (c = i);
the value of i is converted to the type of the assignment expression c = i, that is, char type. The value of the expression enclosed in parentheses is then converted to the type of the outer assignment expression, that is, long int type.
#6
EXAMPLE 3 Consider the fragment: const char **cpp; char *p; const char c = 'A';
cpp = &p; // constraint violation *cpp = &c; // valid *p = 0; // valid
The first assignment is unsafe because it would allow the following valid code to attempt to change the value of the const object c.
#1
For the operators += and -= only, either the left operand shall be a pointer to an object type and the right shall have integer type, or the left operand shall have qualified or unqualified arithmetic type and the right shall have arithmetic type.
#2
For the other operators, each operand shall have arithmetic type consistent with those allowed by the corresponding binary operator.
#3
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.
#1
#2
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.85) If an attempt is made to modify the result of a comma operator or to access it after the next sequence point, the behavior is undefined.
#3
EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists of initializers). 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 (6.7.8).
#1
#2
A constant expression can be evaluated during translation rather than runtime, and accordingly may be used in any place that a constant may be.
#3
Constant expressions shall not contain assignment, increment, decrement, function-call, or comma operators, except when they are contained within a subexpression that is not evaluated.86)
#4
Each constant expression shall evaluate to a constant that is in the range of representable values for its type.
#5
An expression that evaluates to a constant is required in several contexts. If a floating 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.
#6
An integer constant expression87) shall have integer type and shall only have operands that are integer constants, enumeration constants, character constants, sizeof expressions whose results are integer constants, and floating constants that are the immediate operands of casts. Cast operators in an integer constant expression shall only convert arithmetic types to integer types, except as part of an operand to the sizeof operator.
#7
More latitude is permitted for constant expressions in initializers. Such a constant expression shall be, or evaluate to, one of the following:
-- an arithmetic constant expression,
-- a null pointer constant,
-- an address constant, or
-- an address constant for an object type plus or minus an integer constant expression.
#8
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.
#9
An address constant is a null pointer, 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 an integer constant cast to pointer type, 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 of an address constant, but the value of an object shall not be accessed by use of these operators.
#10
An implementation may accept other forms of constant expressions.
#11
The semantic rules for the evaluation of a constant expression are the same as for nonconstant expressions.88)
Forward references: array declarators (6.7.5.2), initialization (6.7.8).
#1
declaration-specifiers init-declarator-listopt ;
storage-class-specifier declaration-specifiersopt
type-specifier declaration-specifiersopt
type-qualifier declaration-specifiersopt
function-specifier declaration-specifiersopt
init-declarator-list , init-declarator
#2
A declaration shall declare at least a declarator (other than the parameters of a function or the members of a structure or union), a tag, or the members of an enumeration.
#3
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 6.7.2.3.
#4
All declarations in the same scope that refer to the same object or function shall specify compatible types.
#5
A declaration specifies the interpretation and attributes of a set of identifiers. A definition of an identifier is a declaration for that identifier that:
-- for an object, causes storage to be reserved for that object;
-- for a function, includes the function body;89)
-- for an enumeration constant or typedef name, is the (only) declaration of the identifier.
#6
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.
#7
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 (6.7.5), enumeration specifiers (6.7.2.2), initialization (6.7.8), tags (6.7.2.3).
#1
typedef
extern
static
auto
register
#2
At most, one storage-class specifier may be given in the declaration specifiers in a declaration.90)
#3
The typedef specifier is called a ``storage-class specifier'' for syntactic convenience only; it is discussed in 6.7.7. The meanings of the various linkages and storage durations were discussed in 6.2.2 and 6.2.4.
#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.91)
#5
The declaration of an identifier for a function that
has block scope shall have no explicit storage-class specifier other than extern.
#6
If an aggregate or union object is declared with a storage-class specifier other than typedef, the properties resulting from the storage-class specifier, except with respect to linkage, also apply to the members of the object, and so on recursively for any aggregate or union member objects.
Forward references: type definitions (6.7.7).
#1
void
char
short
int
long
float
double
signed
unsigned
_Bool
_Complex
_Imaginary
#2
At least one type specifier shall be given in the declaration specifiers in each declaration, and in the specifier-qualifier list in each struct declaration and type name. Each list of type specifiers shall be one of the following sets (delimited by commas, when there is more than
one set on a line); the type specifiers may occur in any order, possibly intermixed with the other declaration specifiers.
-- void
-- char
-- signed char
-- unsigned char
-- short, signed short, short int, or signed short int
-- unsigned short, or unsigned short int
-- int, signed, or signed int
-- unsigned, or unsigned int
-- long, signed long, long int, or signed long int
-- unsigned long, or unsigned long int
-- long long, signed long long, long long int, or signed long long int
-- unsigned long long, or unsigned long long int
-- float
-- double
-- long double
-- _Bool
-- float _Complex
-- double _Complex
-- long double _Complex
-- float _Imaginary
-- double _Imaginary
-- long double _Imaginary
-- struct or union specifier
-- enum specifier -- typedef name
#3
The type specifiers _Complex and _Imaginary shall not be used if the implementation does not provide those types.92)
#4
Specifiers for structures, unions, and enumerations are discussed in 6.7.2.1 through 6.7.2.3. Declarations of typedef names are discussed in 6.7.7. The characteristics of the other types are discussed in 6.2.5.
#5
Each of the comma-separated sets designates the same type, except that for bit-fields, it is implementation- defined whether the specifier int designates the same type as signed int or the same type as unsigned int.
Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.7).
#1
struct-or-union identifieropt { struct-declaration-list }
struct
union
struct-declaration-list struct-declaration
specifier-qualifier-list struct-declarator-list ;
type-specifier specifier-qualifier-listopt
type-qualifier specifier-qualifier-listopt
struct-declarator-list , struct-declarator
declaratoropt : constant-expr
#2
A structure or union shall not contain a member with incomplete or function type (hence, a structure shall not contain an instance of itself, but may contain a pointer to an instance of itself), except that the last member of a structure with more than one named member may have incomplete array type; such a structure (and any union containing, possibly recursively, a member that is such a structure) shall not be a member of a structure or an element of an array.
#3
The expression that specifies the width of a bit-field shall be an integer constant expression that has nonnegative value that shall not exceed the number of bits in an object of the type that is specified if the colon and expression are omitted. If the value is zero, the declaration shall have no declarator.
#4
As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose storage is allocated in an ordered sequence, and a union is a type consisting of a sequence of members whose storage overlap.
#5
Structure and union specifiers have the same form.
#6
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. If the struct-declaration-list contains no named members, the behavior is undefined. The type is incomplete until after the } that terminates the list.
#7
A member of a structure or union may have any object type other than a variably modified type.93) 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;94) its width is preceded by a colon.
#8
A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed int, or unsigned int. A bit-field is interpreted as a signed or unsigned integer type consisting of the specified number of bits.95) If the value 0 or 1 is stored into a nonzero-width bit-field of type _Bool, the value of the bit-field shall compare equal to the value stored.
#9
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.
#10
A bit-field declaration with no declarator, but only a colon and a width, indicates an unnamed bit-field.96) As a special case, a bit-field structure member 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.
#11
Each non-bit-field member of a structure or union object is aligned in an implementation-defined manner appropriate to its type.
#12
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 converted, 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 be unnamed padding within a structure object, but not at its beginning.
#13
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 converted, 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.
#14
There may be unnamed padding at the end of a structure or union.
#15
As a special case, the last element of a structure with more than one named member may have an incomplete array type. This is called a flexible array member, and the size of the structure shall be equal to the offset of the last element of an otherwise identical structure that replaces the flexible array member with an array of unspecified length.97) When an lvalue whose type is a structure with a flexible array member is used to access an object, it behaves as if that member were replaced with the longest array, with the same element type, that would not make the structure larger than the object being accessed; the offset of the array shall remain that of the flexible array member, even if this would differ from that of the replacement array. If this array would have no elements, then it behaves as if it had one element, but the behavior is undefined if any attempt is made to access that element or to generate a pointer one past it.
#16
EXAMPLE Assuming that all array members are aligned the same, after the declarations:
struct s { int n; double d[]; }; struct ss { int n; double d[1]; };
the three expressions:
sizeof (struct s) offsetof(struct s, d) offsetof(struct ss, d)
have the same value. The structure struct s has a flexible array member d.
#17
If sizeof (double) is 8, then after the following code is executed:
struct s *s1; struct s *s2; s1 = malloc(sizeof (struct s) + 64); s2 = malloc(sizeof (struct s) + 46);
and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave as if the identifiers had been declared as:
struct { int n; double d[8]; } *s1; struct { int n; double d[5]; } *s2;
#18
Following the further successful assignments:
s1 = malloc(sizeof (struct s) + 10); s2 = malloc(sizeof (struct s) + 6);
they then behave as if the declarations were:
struct { int n; double d[1]; } *s1, *s2;
and:
double *dp; dp = &(s1->d[0]); // Permitted *dp = 42; // Permitted dp = &(s2->d[0]); // Permitted *dp = 42; // Undefined behavior
Forward references: tags (6.7.2.3).
#1
enum identifieropt { enumerator-list }
enum identifieropt { enumerator-list , }
enum identifier
enumeration-constant = constant-expr
#2
The expression that defines the value of an enumeration constant shall be an integer constant expression that has a value representable as an int.
#3
The identifiers in an enumerator list are declared as constants that have type int and may appear wherever such are permitted.98) 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. (The use of enumerators with = 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.
#4
Each enumerated type shall be compatible with an integer type. The choice of type is implementation-defined,99) but shall be capable of representing the values of all the members of the enumeration. The enumerated type is incomplete until after the } that terminates the list of enumerator declarations.
#5
EXAMPLE The following fragment:
enum hue { chartreuse, burgundy, claret=20, winedark }; enum hue col, *cp; col = claret; cp = &col; if (*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}.
Forward references: tags (6.7.2.3).
#1
A specific type shall have its content defined at most once.
#2
A type specifier of the form
enum identifier
without an enumerator list shall only appear after the type it specifies is completed.
#3
All declarations of structure, union, or enumerated types that have the same scope and use the same tag declare the same type. The type is incomplete100) until the closing brace of the list defining the content, and complete thereafter.
#4
Two declarations of structure, union, or enumerated types which are in different scopes or use different tags declare distinct types. Each declaration of a structure, union, or enumerated type which does not include a tag declares a distinct type.
#5
A type specifier of the form
struct-or-union identifier-opt { struct-declaration-list }
or
enum identifier { enumerator-list }
or
enum identifier { enumerator-list , }
declares a structure, union, or enumerated type. The list defines the structure content, union content, or enumeration content. If an identifier is provided,101) the type specifier also declares the identifier to be the tag of that type.
#6
A declaration of the form
struct-or-union identifier ;
use of that typedef name to declare objects having the specified structure, union, or enumerated type. specifies a structure or union type and declares the identifier as a tag of that type.102)
#7
If a type specifier of the form
struct-or-union identifier
occurs other than as part of one of the above forms, and no other declaration of the identifier as a tag is visible, then it declares an incomplete structure or union type, and declares the identifier as the tag of that type.102)
#8
If a type specifier of the form
struct-or-union identifier
or
enum identifier
occurs other than as part of one of the above forms, and a declaration of the identifier as a tag is visible, then it specifies the same type as that other declaration, and does not redeclare the tag.
#9
EXAMPLE 1 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.
#10
The following alternative formulation uses the typedef mechanism:
typedef struct tnode TNODE; struct tnode { int count; TNODE *left, *right; }; TNODE s, *sp;
#11
EXAMPLE 2 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 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: declarators (6.7.5), array declarators (6.7.5.2), type definitions (6.7.7).
#1
const
restrict
volatile
#2
Types other than pointer types derived from object or incomplete types shall not be restrict-qualified.
#3
The properties associated with qualified types are meaningful only for expressions that are lvalues.103)
#4
If the same qualifier appears more than once in the same specifier-qualifier-list, either directly or via one or more typedefs, the behavior is the same as if it appeared only once.
#5
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.104)
#6
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 5.1.2.3. 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.105) What constitutes an access to an object that has volatile-qualified type is implementation- defined.
#7
An object that is accessed through a restrict-qualified pointer has a special association with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to that object use, directly or indirectly, the value of that particular pointer.106) The intended use of the restrict qualifier (like the register storage class) is to promote optimization, and deleting all instances of the qualifier from a conforming program does not change its meaning (i.e., observable behavior).
#8
If the specification of an array type includes any type qualifiers, the element type is so-qualified, not the array
105A 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.
106For example, a statement that assigns a value returned by malloc to a single pointer establishes this association between the allocated object and the pointer. type. If the specification of a function type includes any type qualifiers, the behavior is undefined.107)
#9
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.
#10
EXAMPLE 1 An object declared
extern const volatile int real_time_clock;
may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.
#11
EXAMPLE 2 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 *''
#1
Let D be a declaration of an ordinary identifier that provides a means of designating an object P as a restrict- qualified pointer.
#2
If D appears inside a block and does not have storage class extern, let B denote the block. If D appears in the list of parameter declarations of a function definition, let B denote the associated block. Otherwise, let B denote the block of main (or the block of whatever function is called at program startup in a freestanding environment).
#3
In what follows, a pointer expression E is said to be based on object P if (at some sequence point in the execution of B prior to the evaluation of E) modifying P to point to a copy of the array object into which it formerly
pointed would change the value of E.108) Note that ``based'' is defined only for expressions with pointer types.
#4
During each execution of B, let A be the array object that is determined dynamically by all accesses through pointer expressions based on P. Then all accesses to values of A shall be through pointer expressions based on P. Furthermore, if P is assigned the value of a pointer expression E that is based on another restricted pointer object P2, associated with block B2, then either the execution of B2 shall begin before the execution of B, or the execution of B2 shall end prior to the assignment. If these requirements are not met, then the behavior is undefined.
#5
Here an execution of B means that portion of the execution of the program during which storage is guaranteed to be reserved for an instance of an object that is associated with B and that has automatic storage duration. An access to a value means either fetching it or modifying it; expressions that are not evaluated do not access values.
#6
A translator is free to ignore any or all aliasing implications of uses of restrict.
#7
EXAMPLE 1 The file scope declarations
int * restrict a; int * restrict b; extern int c[];
assert that if an object is accessed using the value of one of a, b, or c, then it is never accessed using the value of either of the other two.
#8
EXAMPLE 2 The function parameter declarations in the following example
void f(int n, int * restrict p, int * restrict q) { while (n-- > 0) *p++ = *q++; }
assert that, during each execution of the function, if an
object is accessed through one of the pointer parameters, then it is not also accessed through the other.
#9
The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence analysis of function f without examining any of the calls of f in the program. The cost is that the programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through both p and q.
void g(void) { extern int d[100]; f(50, d + 50, d); // ok f(50, d + 1, d); // undefined behavior }
#10
EXAMPLE 3 The function parameter declarations
void h(int n, int * const restrict p, int * const q, int * const r) { int i; for (i = 0; i < n; i++) p[i] = q[i] + r[i]; }
show how const can be used in conjunction with restrict. The const qualifiers imply, without the need to examine the body of h, that q and r cannot become based on p. The fact that p is restrict-qualified therefore implies that an object accessed through p is never accessed through either of q or r. This is the precise assertion required to optimize the loop. Note that a call of the form h(100, a, b, b) has defined behavior, which would not be true if all three of p, q, and r were restrict-qualified.
#11
EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a function call and an equivalent nested block. With one exception, only ``outer-to-inner'' assignments between restricted pointers declared in nested blocks have defined behavior.
{ int * restrict p1; int * restrict q1; p1 = q1; // undefined behavior { int * restrict p2 = p1; // ok int * restrict q2 = q1; // ok p1 = q2; // undefined behavior p2 = q2; // undefined behavior } }
The exception allows the value of a restricted pointer to be carried out of the block in which it (or, more precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For example, this permits new_vector to return a vector.
typedef struct { int n; float * restrict v; } vector; vector new_vector(int n) { vector t; t.n = n; t.v = malloc(n * sizeof (float)); return t; }
#1
inline
#2
Function specifiers shall be used only in the declaration of an identifier for a function.
#3
An inline definition of a function with external linkage shall not contain a definition of a modifiable object with static storage duration, and shall not contain a reference to an identifier with internal linkage.
#4
The inline function specifier shall not appear in a declaration of main.
#5
A function declared with an inline function specifier is an inline function. The function specifier may appear more than once; the behavior is the same as if it appeared only once. Making a function an inline function suggests that calls to the function be as fast as possible.109) The extent to which such suggestions are effective is implementation-defined.110)
#6
Any function with internal linkage can be an inline function. For a function with external linkage, the following restrictions apply: If a function is declared with an inline function specifier, then it shall also be defined in the same translation unit. If all of the file scope declarations for a function in a translation unit include the inline function specifier without extern, then the definition in that translation unit is an inline definition. An inline definition does not provide an external definition for the function, and does not forbid an external definition in another translation unit. An inline definition provides an alternative to an external definition, which a translator may use to implement any call to the function in the same translation unit. It is unspecified whether a call to the function uses the inline definition or the external definition.111)
#7
EXAMPLE The declaration of an inline function with external linkage can result in either an external definition, or a definition available for use only within the translation unit. A file scope declaration with extern creates an external definition. The following example shows an entire translation unit.
111Since an inline definition is distinct from the corresponding external definition and from any other corresponding inline definitions in other translation units, all corresponding objects with static storage duration are also distinct in each of the definitions.
inline double fahr(double t) { return (9.0 * t) / 5.0 + 32.0; } inline double cels(double t) { return (5.0 * (t - 32.0)) / 9.0; } extern double fahr(double); // creates an external definition double convert(int is_fahr, double temp) { /* A translator may perform inline substitutions. */ return is_fahr ? cels(temp) : fahr(temp); }
#8
Note that the definition of fahr is an external definition because fahr is also declared with extern, but the definition of cels is an inline definition. Because cels has external linkage and is referenced, an external definition has to appear in another translation unit (see 6.9); the inline definition and the external definition are distinct and either may be used for the call.
#1
( declarator )
direct-declarator [ assignment-expropt ]
direct-declarator [ * ]
direct-declarator ( parameter-type-list )
direct-declarator ( identifier-listopt )
* type-qualifier-listopt
* type-qualifier-listopt pointer
type-qualifier-list type-qualifier
parameter-type-list:parameter-list , ...
parameter-list , parameter-declaration
declaration-specifiers declarator
declaration-specifiers abstract-declaratoropt
#2
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.
#3
A full declarator is a declarator that is not part of another declarator. The end of a full declarator is a sequence point. If the nested sequence of declarators in a full declarator contains a variable length array type, the type specified by the full declarator is said to be variably modified.
#4
In the following subclauses, 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.
#5
If, in the declaration ``T D1'', D1 has the form
identifier
then the type specified for ident is T.
#6
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 complicated declarators may be altered by parentheses.
Implementation limits
#7
As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and function declarators that modify an arithmetic, structure, union, or incomplete type, either directly or via one or more typedefs.
Forward references: array declarators (6.7.5.2), type definitions (6.7.7).
#1
If, in the declaration ``T D1'', D1 has the form
* type-qualifier-list-opt 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.
#2
For two pointer types to be compatible, both shall be identically qualified and both shall be pointers to compatible types.
#3
EXAMPLE 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 any object pointed to by ptr_to_constant shall not be modified through that pointer, but ptr_to_constant itself may be changed to point to another object. 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.
#4
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''.
#1
The [ and ] may delimit an expression or *. If [ and ] delimit an expression (which specifies the size of an array), it shall have an integer type. If the expression is a constant expression then it shall have a value greater than zero. The element type shall not be an incomplete or function type.
#2
Only ordinary identifiers (as defined in 6.2.3) with both block scope or function prototype scope and no linkage shall have a variably modified type. If an identifier is declared to be an object with static storage duration, it shall not have a variable length array type.
#3
If, in the declaration ``T D1'', D1 has the form
D[assignment-expr-opt]
or
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 array of T''.112) If the size is not present, the array type is an incomplete type. If * is used instead of a size expression, the array type is a variable length array type of unspecified size, which can only be used in declarations with function prototype scope.113) If the size expression is an integer constant expression and the element type has a known constant size, the array type is not a variable length array type; otherwise, the array type is a variable length array type. If the size expression is not a constant expression, and it is evaluated at program execution time, it shall evaluate to a value greater than zero. It is unspecified whether side effects are produced when the size expression is evaluated. The size of each instance of a variable length array type does not change during its lifetime.
compatible element types, and if both size specifiers are present, and are integer constant expressions, then both size specifiers shall have the same constant value. If the two array types are used in a context which requires them to be compatible, it is undefined behavior if the two size specifiers evaluate to unequal values.
#5
EXAMPLE 1
float fa[11], *afp[17];
declares an array of float numbers and an array of pointers to float numbers.
#6
EXAMPLE 2 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.
#7
EXAMPLE 3 The following declarations demonstrate the compatibility rules for variably modified types.
extern int n; extern int m; void fcompat(void) { int a[n][6][m]; int (*p)[4][n+1]; int c[n][n][6][m]; int (*r)[n][n][n+1]; p = a; // Error - not compatible because 4 != 6. r = c; // Compatible, but defined behavior // only if n == 6 and m == n+1. }
#8
EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or function prototype scope. Array objects declared with the static or extern storage class specifier cannot have a variable length array (VLA) type. However, an object declared with the static storage class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of structures or unions.
extern int n; int A[n]; // Error - file scope VLA. extern int (*p2)[n]; // Error - file scope VM. int B[100]; // OK - file scope but not VM. void fvla(int m, int C[m][m]) // OK - VLA with prototype scope. { typedef int VLA[m][m] // OK - block scope typedef VLA. struct tag { int (*y)[n]; // Error - y not ordinary identifier. int z[n]; // Error - z not ordinary identifier. }; int D[m]; // OK - auto VLA. static int E[m]; // Error - static block scope VLA. extern int F[m]; // Error - F has linkage and is VLA. int (*s)[m]; // OK - auto pointer to VLA. extern int (*r)[m]; // Error - r had linkage and is // a pointer to VLA. static int (*q)[m] = &B; // OK - q is a static block // pointer to VLA. }
Forward references: function declarators (6.7.5.3), function definitions (6.9.1), initialization (6.7.8).
#1
A function declarator shall not specify a return type that is a function type or an array type.
#2
The only storage-class specifier that shall occur in a parameter declaration is register.
#3
An identifier list in a function declarator that is not part of a definition of that function shall be empty.
#4
After adjustment, the parameters in a parameter type list in a function declarator that is part of a definition of that function shall not have incomplete type.
#5
If, in the declaration ``T D1'', D1 has the form
D(parameter-type-list)
or
D(identifier-list-opt)
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''.
#6
A parameter type list specifies the types of, and may declare identifiers for, the parameters of the function. 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 6.3.2.1. If the list terminates with an ellipsis (, ...), no information about the number or types of the parameters after the comma is supplied.114) The special case of an unnamed parameter of type void as the only item in the list specifies that the function has no parameters.
#7
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.
#8
If the function declarator is not part of a definition of that function, parameters may have incomplete type and may use the [*] notation in their sequences of declarator specifiers to specify variable length array types.
#9
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.
#10
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 definition of that function specifies that the function has no parameters. The empty list in a function declarator that is not part of a definition of that function specifies that no information about the number or types of the parameters is supplied.115)
#11
For two function types to be compatible, both shall specify compatible return types.116) 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. (In the determination of type compatibility and of a composite type, each parameter declared with function or array type is taken as having the adjusted type and each parameter declared with qualified type is taken as having the unqualified version of its declared type.)
#12
EXAMPLE 1 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.
#13
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 either internal or external linkage (depending on what file scope declarations for these identifiers are visible), and the identifier of the pointer pfi has block scope and no linkage.
#14
EXAMPLE 2 The declaration
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.
#15
EXAMPLE 3 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 int), and an int. The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more additional arguments of any type.
#16
EXAMPLE 4 The following prototype has a variably modified parameter.
void addscalar(int n, int m, double a[n][n*m+300], double x); int main() { double b[4][308]; addscalar(4, 2, b, 2.17); return 0; } void addscalar(int n, int m, double a[n][n*m+300], double x) { for (int i = 0; i < n; i++) for (int j = 0, k = n*m+300; j < k; j++) // a is a pointer to a VLA // with n*m+300 elements a[i][j] += x; }
#17
EXAMPLE 5 The following are all compatible function prototype declarators.
double maximum(int n, int m, double a[n][m]); double maximum(int n, int m, double a[*][*]); double maximum(int n, int m, double a[ ][*]); double maximum(int n, int m, double a[ ][m]);
Forward references: function definitions (6.9.1), type names (6.7.6).
#1
specifier-qualifier-list abstract-declaratoropt
pointeropt direct-abstract-declarator
direct-abstract-declaratoropt [ assignment-expropt ]
direct-abstract-declaratoropt [ * ]
direct-abstract-declaratoropt ( parameter-type-listopt )
#2
In several contexts, it is necessary 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.117)
#3
EXAMPLE The constructions
(a) int (b) int * (c) int *[3] (d) int (*)[3] (e) int (*)[*] (f) int *() (g) int (*)(void) (h) 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 ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function with no parameter specification returning a pointer to int, (g) pointer to function with no parameters returning an int, and (h) 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.
#1
#2
If a typedef name specifies a variably modified type then it shall have block scope.
#3
In a declaration whose storage-class specifier is typedef, each declarator defines an identifier to be a typedef name that denotes the type specified for the identifier in the way described in 6.7.5. Any array size expressions associated with variable length array declarators are evaluated each time the declaration of the typedef name is reached in the order of execution. 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.
#4
EXAMPLE 1 After
typedef int MILES, KLICKSP(); typedef struct { double hi, lo; } range;
the constructions
MILES distance; extern KLICKSP *metricp; range x; range 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.
#5
EXAMPLE 2 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, or int.
#6
EXAMPLE 3 The following obscure 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.) The first two bit-field declarations differ in that unsigned is a type specifier (which forces t to be the name of a structure member), while const is a type qualifier (which modifies t which is still visible as a typedef name). 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 int.
#7
EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the following declarations of the signal function specify exactly the same type, the first without making use of any typedef names.
typedef void fv(int), (*pfv)(int); void (*signal(int, void (*)(int)))(int); fv *signal(int, fv *); pfv signal(int, pfv);
#8
EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the time the typedef name is defined, not each time it is used:
void copyt(int n) { typedef int B[n]; // B is n ints, n evaluated now. n += 1; B a; // a is n ints, n without += 1. int b[n]; // a and b are different sizes for (int i = 1; i < n; i++) a[i-1] = b[i]; }
Forward references: the signal function (7.14.1.1).
#1
{ initializer-list }
{ initializer-list , }
initializer-list , designationopt initializer
[ constant-expr ]
#2
No initializer shall attempt to provide a value for an object not contained within the entity being initialized.
#3
The type of the entity to be initialized shall be an array of unknown size or an object type that is not a variable length array type.
#4
All the expressions in an initializer for an object that has static storage duration shall be constant expressions or string literals.
#5
If the declaration of an identifier has block scope, and the identifier has external or internal linkage, the declaration shall have no initializer for the identifier.
#6
If a designator has the form
[ constant-expr ]
then the current object (defined below) shall have array type and the expression shall be an integer constant expression. If the array is of unknown size, any nonnegative value is valid.
#7
If a designator has the form
. identifier
then the current object (defined below) shall have structure or union type and the identifier shall be the name of a member of that type.
#8
An initializer specifies the initial value stored in an object.
#9
Except where explicitly stated otherwise, for the purposes of this subclause unnamed members of objects of structure and union type do not participate in initialization. Unnamed members of structure objects have indeterminate value even after initialization.
#10
If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate. If an object that has static storage duration is not initialized explicitly, then:
-- if it has pointer type, it is initialized to a null pointer;
-- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
-- if it is an aggregate, every member is initialized (recursively) according to these rules;
-- if it is a union, the first named member is initialized (recursively) according to these rules.
#11
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 (after conversion); the same type constraints and conversions as for simple assignment apply, taking the type of the scalar to be the unqualified version of its declared type.
#12
The rest of this subclause deals with initializers for objects that have aggregate or union type.
#13
The initializer for a structure or union object that has automatic storage duration shall be either an initializer list as described below, or a single expression that has compatible structure or union type. In the latter case, the initial value of the object, including unnamed members, is that of the expression.
#14
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 elements of the array.
#15
An array with element type compatible with wchar_t may be initialized by a wide string literal, optionally enclosed in braces. Successive wide characters of the wide string literal (including the terminating null wide character if there is room or if the array is of unknown size) initialize the elements of the array.
#16
Otherwise, the initializer for an object that has aggregate or union type shall be a brace-enclosed list of initializers for the elements or named members.
#17
Each brace-enclosed initializer list has an associated current object. When no designations are present, subobjects of the current object are initialized in order according to the type of the current object: array elements in increasing subscript order, structure members in declaration order, and the first named member of a union.118) In contrast, a designation causes the following initializer to begin initialization of the subobject described by the designator. Initialization then continues forward in order, beginning with the next subobject after that described by the designator.119)
#18
Each designator list begins its description with the current object associated with the closest surrounding brace pair. Each item in the designator list (in order) specifies a particular member of its current object and changes the current object for the next designator (if any) to be that member.120) The current object that results at the end of the designator list is the subobject to be initialized by the following initializer.
#19
The initialization shall occur in initializer list order, each initializer provided for a particular subobject overriding any previously listed initializer for the same subobject; all subobjects that are not initialized explicitly shall be initialized implicitly the same as objects that have static storage duration.
#20
If the aggregate or union contains elements or members that are aggregates or unions, these 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 elements or members of the subaggregate or the contained union. Otherwise, only enough initializers from the list are taken to account for the elements or members of the subaggregate or the first member of the contained union; any remaining initializers are left to initialize the next element or member of the aggregate of which the current subaggregate or contained union is a part.
#21
If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration.
#22
If an array of unknown size is initialized, its size is determined by the largest indexed element with an explicit initializer. At the end of its initializer list, the array no longer has incomplete type.
#23
The order in which any side effects occur among the
initialization list expressions is unspecified.121)
#24
EXAMPLE 1 Provided that <complex.h> has been #included, the declarations
int i = 3.5; complex c = 5 + 3 * I;
define and initialize i with the value 3 and c with the value 5.0+3.0i.
#25
EXAMPLE 2 The declaration
int x[] = { 1, 3, 5 };
defines and initializes x as a one-dimensional array object that has three elements, as no size was specified and there are three initializers.
#26
EXAMPLE 3 The declaration
int 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 y (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
int 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].
#27
EXAMPLE 4 The declaration
int z[4][3] = { { 1 }, { 2 }, { 3 }, { 4 } };
initializes the first column of z as specified and initializes the rest with zeros.
#28
EXAMPLE 5 The declaration
struct { int a[3], b; } w[] = { { 1 }, 2 };
is a definition with an inconsistently bracketed initialization. It defines an array with two element structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.
#29
EXAMPLE 6 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] 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 elements are initialized with zero. Likewise, the initializers for q[1][0] and q[2][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 have been issued. 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.
#30
Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to cause confusion.
#31
EXAMPLE 7 One form of initialization that completes array types involves typedef names. Given the declaration
typedef int A[]; // OK - declared with block scope
the declaration
A a = { 1, 2 }, b = { 3, 4, 5 };
is identical to
int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
due to the rules for incomplete types.
#32
EXAMPLE 8 The declaration
char s[] = "abc", t[3] = "abc";
defines ``plain'' char array objects s and t whose elements 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'' and initializes it to point to an object with type ``array of char'' with length 4 whose elements 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.
#33
EXAMPLE 9 Arrays can be initialized to correspond to the elements of an enumeration by using designators:
enum { member_one, member_two }; const char *nm[] = { [member_two] = "member two", [member_one] = "member one", };
#34
EXAMPLE 10 Structure members can be initialized to nonzero values without depending on their order:
div_t answer = { .quot = 2, .rem = -1 };
#35
EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists might be misunderstood:
struct { int a[3], b; } w[] = { [0].a = {1}, [1].a[0] = 2 };
#36
EXAMPLE 12 Space can be ``allocated'' from both ends of an array by using a single designator:
int a[MAX] = { 1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0 };
#37
In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less than ten, some of the values provided by the first five initializers will be overridden by the second five.
#38
EXAMPLE 13 Any member of a union can be initialized:
union { /* ... */ } u = { .any_member = 42 };
Forward references: common definitions <stddef.h> (7.17).
#1
#2
A statement specifies an action to be performed. Except as indicated, statements are executed in sequence.
#3
A block allows a set of declarations and statements to be grouped into one syntactic unit. The initializers of objects that have automatic storage duration, and the variable length array declarators of ordinary identifiers with block scope, are evaluated and the values are stored in the objects (including storing an indeterminate value in objects without an initializer) each time the declaration is reached in the order of execution, as if it were a statement, and within each declaration in the order that declarators appear.
#4
A full expression is an expression that is not part of another expression or declarator. 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 (optional) expressions of a for statement; the (optional) expression in a return statement. The end of a full expression is a sequence point.
Forward references: expression and null statements (6.8.3), selection statements (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
#1
case constant-expr : statement
default : statement
#2
A case or default label shall appear only in a switch statement. Further constraints on such labels are discussed under the switch statement.
#3
Label names shall be unique within a function.
#4
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 (6.8.6.1), the switch statement (6.8.4.2).
#1
{ block-item-listopt }
#2
A compound statement is a block.
#1
expressionopt ;
#2
The expression in an expression statement is evaluated as a void expression for its side effects.122)
#3
A null statement (consisting of just a semicolon) performs no operations.
#4
EXAMPLE 1 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);
#5
EXAMPLE 2 In the program fragment
char *s; /* ... */ while (*s++ != '\0') ;
a null statement is used to supply an empty loop body to the iteration statement.
#6
EXAMPLE 3 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 (6.8.5).
#1
if ( expression ) statement
if ( expression ) statement else statement
switch ( expression ) statement
#2
A selection statement selects among a set of statements depending on the value of a controlling expression.
#3
A selection statement is a block whose scope is a strict subset of the scope of its enclosing block. Each associated substatement is also a block whose scope is a strict subset of the scope of the selection statement.
#1
The controlling expression of an if statement shall have scalar type.
#2
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.
#3
An else is associated with the lexically nearest preceding if that is allowed by the syntax.
#1
The controlling expression of a switch statement shall have integer type.
#2
If a switch statement has an accessible case or default label within the scope of an identifier with a variably modified type, the entire switch statement shall be within the scope of that identifier.123)
#3
The expression of each case label shall be an integer constant expression and 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.)
#4
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.
#5
The integer 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.
Implementation limits
#6
As discussed in 5.2.4.1, the implementation may limit the number of case values in a switch statement.
#7
EXAMPLE In the artificial program fragment
switch (expr) { int i = 4; f(i); case 0: i = 17; /* falls through into default code */ default: printf("%d\n", i); }
the object whose identifier is i exists with automatic storage duration (within the block) but is never initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will access
an indeterminate value. Similarly, the call to the function f cannot be reached.
#1
while ( expression ) statement
do statement while ( expression ) ;
for ( expropt ; expropt ; expropt ) statement
for ( declaration expropt ; expropt ) statement
#2
The controlling expression of an iteration statement shall have scalar type.
#3
The declaration part of a for statement shall only declare identifiers for objects having storage class auto or register.
#4
An iteration statement causes a statement called the loop body to be executed repeatedly until the controlling expression compares equal to 0.
#5
An iteration statement is a block whose scope is a strict subset of the scope of its enclosing block. The loop body is also a block whose scope is a strict subset of the scope of the iteration statement.
#1
The evaluation of the controlling expression takes place before each execution of the loop body.
#1
The evaluation of the controlling expression takes place after each execution of the loop body.
#1
The statement
for ( clause-1 ; expr-2 ; expr-3 ) statement
behaves as follows: The expression expr-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expr-3 is evaluated as a void expression after each execution of the loop body. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.124)
#2
Both clause-1 and expr-3 can be omitted. An omitted expr-2 is replaced by a nonzero constant.
#1
goto identifier ;
continue ;
break ;
return expressionopt ;
#2
A jump statement causes an unconditional jump to another place.
#1
The identifier in a goto statement shall name a label located somewhere in the enclosing function. A goto statement shall not jump from outside the scope of an identifier having a variably modified type to inside the scope of that identifier.
#2
A goto statement causes an unconditional jump to the statement prefixed by the named label in the enclosing function.
#3
EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The following outline presents one possible approach to a problem based on these three assumptions:
1. The general initialization code accesses objects only visible to the current function.
2. The general initialization code is too large to warrant duplication.
3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by continue statements, for example.)
/* ... */ goto first_time; for (;;) { // determine next operation /* ... */ if (need to reinitialize) { // reinitialize-only code /* ... */ first_time: // general initialization code /* ... */ continue; } // handle other operations /* ... */ }
#4
EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably modified types. A jump within the scope, however, is permitted. goto lab3; // Error: going INTO scope of VLA. { double a[n]; a[j] = 4.4; lab3: a[j] = 3.3; goto lab4; // OK, going WITHIN scope of VLA. a[j] = 5.5; lab4: a[j] = 6.6; } goto lab4; // Error: going INTO scope of VLA.
#1
A continue statement shall appear only in or as a loop body.
#2
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;.125)
#1
A break statement shall appear only in or as a switch body or loop body.
#2
A break statement terminates execution of the smallest enclosing switch or iteration statement.
#1
A return statement with an expression shall not appear in a function whose return type is void. A return statement without an expression shall only appear in a function whose return type is void.
#2
A return statement terminates execution of the current function and returns control to its caller. A function may have any number of return statements.
#3
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 the return type of the function in which it appears, the value is converted as if by assignment to an object having the return type of the function.126)
#4
EXAMPLE In:
struct s { double i; } f(void); union { struct { int f1; struct s f2; } u1; struct { struct s f3; int f4; } u2; } g; struct s f(void) { return g.u1.f2; } /* ... */ g.u2.f3 = f();
there is no undefined behavior, although there would be if the assignment were done directly (without using a function call to fetch the value).
#1
translation-unit external-declaration
#2
The storage-class specifiers auto and register shall not appear in the declaration specifiers in an external declaration.
#3
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.
#4
As discussed in 5.1.1.1, 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 6.7, a declaration that also causes storage to be reserved for an object or a function named by the identifier is a definition.
#5
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; otherwise, there shall be no more than one.127)
#1
declaration-specifiers declarator declaration-listopt compound-statement
#2
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.128)
#3
The return type of a function shall be void or an object type other than array type.
#4
The storage-class specifier, if any, in the declaration specifiers shall be either extern or static.
#5
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 case there shall not be an identifier. No declaration list shall follow.
#6
If the declarator includes an identifier list, each declaration in the declaration list shall have at least one declarator, those declarators shall declare only identifiers from the identifier list, and every identifier in the identifier list shall be declared. 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.
#7
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,129) the types of the parameters shall be declared in a following declaration list. In either case, the type of each parameter is adjusted as described in 6.7.5.3 for a parameter type list; the resulting type shall be an object type.
#8
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.
#9
Each parameter has automatic storage duration. Its identifier is an lvalue, which is in effect declared at the head of the compound statement that constitutes the function body (and therefore cannot be redeclared in the function body except in an enclosed block). The layout of the storage for parameters is unspecified.
#10
On entry to the function, the size expressions of each variably modified parameter are evaluated and the value of each argument expression is converted to the type of the corresponding parameter as if by assignment. (Array expressions and function designators as arguments were converted to pointers before the call.)
#11
After all parameters have been assigned, the compound statement that constitutes the body of the function definition is executed.
#12
If the } that terminates a function is reached, and the value of the function call is used by the caller, the behavior is undefined.
#13
EXAMPLE 1 In the following:
extern int max(int a, int b) { return a > b ? a : b; }
extern is the storage-class specifier and int is the type specifier; 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. 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 does not.
#14
EXAMPLE 2 To pass one function to another, one might say
int f(void); /* ... */ g(f);
Then the definition of g might read
void g(int (*funcp)(void)) { /* ... */ (*funcp)() /* or funcp() ... */ }
or, equivalently,
void g(int func(void)) { /* ... */ func() /* or (*func)() ... */ }
#1
If the declaration of an identifier for an object has file scope and an initializer, the declaration is an external definition for the identifier.
#2
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.
#3
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.
#4
EXAMPLE 1
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; // 6.2.2 renders undefined, linkage disagreement int i3; // valid tentative definition, refers to previous int i4; // valid tentative definition, refers to previous int i5; // 6.2.2 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
#5
EXAMPLE 2 If at the end of the translation unit containing
int i[];
the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to zero on program startup.
#1
groupopt
if-group elif-groupsopt else-groupopt endif-line
# if constant-expr new-line groupopt
# ifdef identifier new-line groupopt
# ifndef identifier new-line groupopt
# elif constant-expr new-line groupopt
# endif new-line
# define identifier replacement-list new-line
# define identifier lparen identifier-listopt ) replacement-list new-line
# define identifier lparen ... ) replacement-list new-line
# define identifier lparen identifier-list , ... ) replacement-list new-line
# undef identifier new-line
# pragma pp-tokensopt new-line
# new-line
a ( character not immediately preceded by white-space
pp-tokensopt
the new-line character
#2
A preprocessing directive consists of a sequence of preprocessing tokens that begins with a # preprocessing token that (at the start of translation phase 4) 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.130) A new-line character ends the preprocessing directive even if it occurs within what would otherwise be an invocation of a function-like macro.
#3
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 or possibly other white-space characters in translation phase 3).
#4
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.
#5
The preprocessing tokens within a preprocessing directive are not subject to macro expansion unless
otherwise stated.
#6
EXAMPLE In:
#define EMPTY EMPTY # include <file.h>
the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been replaced.
#1
The expression that controls conditional inclusion shall be an integer constant expression except that: it shall not contain a cast; identifiers (including those lexically identical to keywords) are interpreted as described below;131) and it may contain unary operator expressions of the form
defined identifier
or
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.
#2
Preprocessing directives of the forms
# if constant-expr new-line group-opt # elif constant-expr new-line group-opt
check whether the controlling constant expression evaluates to nonzero.
#3
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 or use of the defined unary operator does not match one of the two specified forms prior to macro replacement, the behavior is undefined. After all replacements due to macro expansion and the defined unary operator have been performed, all remaining identifiers are replaced with the pp-number 0, and then each preprocessing token is converted into a token. The resulting tokens compose the controlling constant expression which is evaluated according to the rules of 6.6, except that all signed integer types and all unsigned integer types act as if they have the same representation as, respectively, the types intmax_t and uintmax_t defined in the header <stdint.h>. 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.132) Also, whether a single- character character constant may have a negative value is implementation-defined.
#4
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.
#5
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.133)
Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest integer types (7.18.1.5).
#1
A #include directive shall identify a header or source file that can be processed by the implementation.
#2
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.
#3
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.
#4
A preprocessing directive of the form
# include pp-tokens new-line
(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.134) 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.
#5
The implementation shall provide unique mappings for sequences consisting of one or more letters or digits (as defined in 5.2.1) followed by a period (.) and a single letter. The first character shall be a letter. The implementation may ignore the distinctions of alphabetical case and restrict the mapping to eight significant characters before the period.
#6
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 5.2.4.1).
#7
EXAMPLE 1 The most common uses of #include preprocessing directives are as in the following:
#include <stdio.h> #include "myprog.h"
#8
EXAMPLE 2 This illustrates macro-replaced #include directives:
#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 (6.10.3).
#1
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.
#2
An identifier currently defined as a macro without use
of lparen (an object-like macro) shall not be redefined by another #define preprocessing directive unless the second definition is an object-like macro definition and the two replacement lists are identical.
#3
An identifier currently defined as a macro using lparen (a function-like macro) shall not be redefined by another #define preprocessing directive unless 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.
#4
If the identifier-list in the macro definition does not end with an ellipsis, the number of arguments, including those arguments consisting of no preprocessing tokens, in an invocation of a function-like macro shall agree with the number of parameters in the macro definition. Otherwise, there shall be more arguments in the invocation than there are parameters in the macro definition (excluding the ...). There shall exist a ) preprocessing token that terminates the invocation.
#5
The identifier __VA_ARGS__ shall only occur in the replacement-list of a #define preprocessing directive using the ellipsis notation in the arguments.
#6
A parameter identifier in a function-like macro shall be uniquely declared within its scope.
#7
The identifier immediately following the define is called the macro name. There is one name space for macro names. 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.
#8
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.
#9
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 name135) to be replaced by the replacement list of preprocessing tokens that constitute the remainder of the directive.
#10
A preprocessing directive of the form # define identifier lparen identifier-list-opt ) replacement-list new-line # define identifier lparen ... ) replacement-list new-line # define identifier lparen identifier-list , ... ) 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.
#11
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 between matching inner parentheses do not separate arguments. If there are sequences of preprocessing tokens within the list of arguments that would otherwise act as preprocessing directives, the behavior is undefined.
#12
If there is a ... in the identifier-list in the macro definition, then the trailing arguments, including any separating comma preprocessing tokens, are merged to form a single item: the variable arguments. The number of arguments so combined is such that, following merger, the number of arguments is one more than the number of parameters in the macro definition (excluding the ...).
#1
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 preprocessing file; no other preprocessing tokens are available.
#2
An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it were a parameter, and the variable arguments shall form the preprocessing tokens used to replace it.
#1
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.
#2
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 composing 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), except that it is unspecified whether a \ character is inserted before the \ character beginning a universal character name. If the replacement that results is not a valid character string literal, the behavior is undefined. The character string literal corresponding to an empty argument is "". The order of evaluation of # and ## operators is unspecified.
#1
A ## preprocessing token shall not occur at the beginning or at the end of a replacement list for either form of macro definition.
#2
If, in the replacement list of a function-like macro, a parameter is immediately preceded or followed by a ## preprocessing token, the parameter is replaced by the corresponding argument's preprocessing token sequence; however, if an argument consists of no preprocessing tokens, the parameter is replaced by a placemarker preprocessing token instead.
#3
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. Placemarker preprocessing tokens are handled specially: concatenation of two placemarkers results in a single placemarker preprocessing token, and concatenation of a placemarker with a non-placemarker preprocessing token results in the non-placemarker 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.
#4
EXAMPLE In the following fragment:
#define hash_hash # ## # #define mkstr(a) # a #define in_between(a) mkstr(a) #define join(c, d) in_between(c hash_hash d) char p[] = join(x, y); // equivalent to // char p[] = "x ## y";
The expansion produces, at various stages: join(x, y)
in_between(x hash_hash y) in_between(x ## y) mkstr(x ## y) "x ## y"
In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but this new token is not the ## operator.
#1
After all parameters in the replacement list have been substituted and # and ## processing has taken place, all placemarker preprocessing tokens are removed. Then, the resulting preprocessing token sequence is rescanned, along with all subsequent preprocessing tokens of the source file, for more macro names to replace.
#2
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.
#3
The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one, but all pragma unary operator expressions within it are then processed as specified in 6.10.9 below.
#1
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 preprocessing translation unit. Macro definitions have no significance after translation phase 4.
#2
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.
#3
EXAMPLE 1 The simplest use of this facility is to define a ``manifest constant'', as in
#define TABSIZE 100 int table[TABSIZE];
#4
EXAMPLE 2 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 generating more code than a function if invoked several times. It also cannot have its address taken, as it has none.
#define max(a, b) ((a) > (b) ? (a) : (b))
The parentheses ensure that the arguments and the resulting expression are bound properly.
#5
EXAMPLE 3 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 #define p() int #define q(x) x #define r(x,y) x ## y #define str(x) # x f(y+1) + f(f(z)) % t(t(g)(0) + t)(1); g(x+(3,4)-w) | h 5) & m (f)^m(m); p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) }; char c[2][6] = { str(hello), str() };
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); int i[] = { 1, 23, 4, 5, }; char c[2][6] = { "hello", "" };
#6
EXAMPLE 4 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 "