History and outlook
The first standard for C was published by ANSI. Although this document was subsequently adopted by ISO/IEC and subsequent revisions published by ISO/IEC have been adopted by ANSI, "ANSI C" is still used to refer to the standard. While some software developers use the term ISO C, others are standards-body neutral and use Standard C.Standardizing C
In 1983, the American National Standards Institute formed a committee, X3J11, to establish a standard specification of C. In 1985, the first Standard Draft was released, sometimes referred to as ''C85''. In 1986, another Draft Standard was released, sometimes referred to as ''C86''. The prerelease Standard C was published in 1988, and sometimes referred to as ''C88''.C89
The ANSI standard was completed in 1989 and ratified as ANSI X3.159-1989 "Programming Language C." This version of the language is often referred to as "ANSI C". Later on sometimes the label "C89" is used to distinguish it from C90 but using the same labeling method.C90
The same standard as C89 was ratified by ISO/IEC as ISO/IEC 9899:1990, with only formatting changes, which is sometimes referred to as C90. Therefore, the terms "C89" and "C90" refer to essentially the same language. This standard has been withdrawn by both ANSI/INCITS and ISO/IEC.C95
In 1995, the ISO/ IEC published an extension, called Amendment 1, for the ANSI-C standard. Its full name finally was ''ISO/IEC 9899:1990/AMD1:1995'' or nicknamed ''C95''. Aside from error correction there were further changes to the language capabilities, such as: * Improved ''multi-byte'' and '' wide character'' support in the standard library, introducingand for &&
* Specification of the standard macro __STDC_VERSION__
In addition to the amendment, two technical corrigenda were published by ISO for C90:
* ISO/IEC 9899:1990/Cor 1:1994 TCOR1 in 1994
* ISO/IEC 9899:1990/Cor 2:1996 in 1996
Preprocessor test for C95 compatibility
C99
In March 2000, ANSI adopted the ISO/IEC 9899:1999 standard. This standard is commonly referred to as C99. Some notable additions to the previous standard include: * New built-in data types:long long, _Bool, _Complex, and _Imaginary
* Several new core language features, including static array indices, designated initializers, compound literals, variable-length arrays, flexible array members, variadic macros, and restrict keyword
* Several new library headers, including stdint.h
In the C programming language, data types constitute the semantics and characteristics of storage of data elements. They are expressed in the language syntax in form of declarations for memory locations or variables. Data types also determin ...
, <tgmath.h>, fenv.h, <complex.h>
* Improved compatibility with several C++ features, including inline functions, single-line //, mixing declarations and code, and universal character names in identifiers
* Removed several dangerous C89 language features such as implicit function declarations and implicit int
Three technical corrigenda were published by ISO for C99:
* ISO/IEC 9899:1999/Cor 1:2001(E)
* ISO/IEC 9899:1999/Cor 2:2004(E)
* ISO/IEC 9899:1999/Cor 3:2007(E), notable for deprecating the standard library function gets
This standard has been withdrawn by both ANSI/INCITS and ISO/IEC in favour of C11.
C11
C11 was officially ratified and published on December 8, 2011. Notable features include improved Unicode support, type-generic expressions using the new_Generic keyword, a cross-platform multi-threading API (threads.h), and atomic types support in both core language and the library (stdatomic.h).
One technical corrigendum has been published by ISO for C11:
* ISO/IEC 9899:2011/Cor 1:2012
C17
, "C17" is the current standard for theC2x
C2x is an informal name for the next (after C17) major C language standard revision.Other related ISO publications
As part of the standardization process, ISO/IEC also publishes technical reports and specifications related to the C language: * ISO/IEC TR 19769:2004, on library extensions to support Unicode transformation formats, integrated into C11 * ISO/IEC TR 24731-1:2007, on library extensions to support bounds-checked interfaces, integrated into C11 * ISO/IEC TR 18037:2008, on embedded C extensions * ISO/IEC TR 24732:2009, on decimal floating point arithmetic, superseded by ISO/IEC TS 18661-2:2015 * ISO/IEC TR 24747:2009, on special mathematical functions, * ISO/IEC TR 24731-2:2010, on library extensions to support dynamic allocation functions * ISO/IEC TS 17961:2013, on secure coding in C * ISO/IEC TS 18661-1:2014, on IEC 60559:2011-compatible binary floating-point arithmetic * ISO/IEC TS 18661-2:2015, on IEC 60559:2011-compatible decimal floating point arithmetic * ISO/IEC TS 18661-3:2015, on IEC 60559:2011-compatible interchange and extended floating-point types * ISO/IEC TS 18661-4:2015, on IEC 60559:2011-compatible supplementary functions More technical specifications are in development and pending approval, including the fifth and final part of TS 18661, a software transactional memory specification, and parallel library extensions.Support from major compilers
ANSI C is now supported by almost all the widely used compilers. GCC and Clang are two major C compilers popular today, both are based on the C11 with updates including changes from later specifications such as C17 and C18. Any source code written ''only'' in standard C and without any hardware dependent assumptions is virtually guaranteed to compile correctly on any platform with a conforming C implementation. Without such precautions, most programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to the reliance on compiler- or platform-specific attributes such as the exact size of certain data types and byte endianness.Compliance detectability
To mitigate the differences between K&R C and the ANSI C standard, the__STDC__ ("standard c") macro can be used to split code into ANSI and K&R sections.
__STDC__ to zero to indicate non-ANSI compliance.
Compilers supporting ANSI C
* Amsterdam Compiler Kit (C K&R and C89/90) * ARM RealView * Clang, using LLVM backend * GCC (full C89/90, C99 and C11) * HP C/ANSI C compiler (C89 and C99) * IBM XL C/C++ (C11, starting with version 12.1) * Intel's ICC *See also
* Behavioral Description Language * Compatibility of C and C++ *References
Further reading
*External links