Foreword

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. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of the joint technical committee is to prepare International Standards. 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.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.

ISO/IEC 9899 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee SC 22, Programming languages, their environments and system software interfaces.

This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, which has been technically revised. It also incorporates the Technical Corrigenda ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:

— conditional (optional) features (including some that were previously mandatory)
— support for multiple threads of execution including an improved memory sequencing model, atomic objects, and thread-local storage (<stdatomic.h> and <threads.h>)
— additional floating-point characteristic macros (<float.h>)
— querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
— Unicode characters and strings (<uchar.h>) (originally specified in ISO/IEC TR 19769:2004)
— type-generic expressions
— static assertions
— anonymous structures and unions
— no-return functions
— macros to create complex numbers (<complex.h>)
— support for opening files for exclusive access
— removed the gets function (<stdio.h>)
— added the aligned_alloc, at_quick_exit, and quick_exit functions (<stdlib.h>)
— (conditional) support for bounds-checking interfaces (originally specified in ISO/IEC TR 24731−1:2007)
— (conditional) support for analyzability

Major changes in the second edition included:

— restricted character set support via digraphs and <iso646.h> (originally specified in ISO/IEC 9899:1990/Amd.1:1995)
— wide character library support in <wchar.h> and <wctype.h> (originally specified in ISO/IEC 9899:1990/Amd.1:1995)
— more precise aliasing rules via effective type
— restricted pointers
— variable length arrays
— flexible array members
— static and type qualifiers in parameter array declarators
— complex (and imaginary) support in <complex.h>
— type-generic math macros in <tgmath.h>
— the long long int type and library functions
— extended integer types
— increased minimum translation limits
— additional floating-point characteristics in <float.h>
— remove implicit int
— reliable integer division
— universal character names (\u and \U)
— extended identifiers
— hexadecimal floating-point constants and %a and %A printf/scanf conversion specifiers
— compound literals
— designated initializers
— // comments
— specified width integer types and corresponding library functions in <inttypes.h> and <stdint.h>
— remove implicit function declaration
— preprocessor arithmetic done in intmax_t/uintmax_t
— mixed declarations and statements
— new block scopes for selection and iteration statements
— integer constant type rules
— integer promotion rules
— macros with a variable number of arguments
— the vscanf family of functions in <stdio.h> and <wchar.h>
— additional math library functions in <math.h>
— treatment of error conditions by math library functions (math_errhandling)
— 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 in <stdio.h>
— boolean type in <stdbool.h>
— idempotent type qualifiers
— empty macro arguments
— new structure type compatibility rules (tag compatibility)
— additional predefined macro names
— _Pragma 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
— conversion of array to pointer not limited to lvalues
— relaxed constraints on aggregate and union initialization
— relaxed restrictions on portable header names
— return without expression not permitted in function that returns a value (and vice versa)

BS ISO/IEC 9899:2011

Information technology. Programming languages. C

Published:

31 Mar 2012

Withdrawn:

13 Jul 2018