ANSI C, ISO C, and Standard C are successive standards for the

C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language, as well a ...

published by the

American National Standards Institute The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

(ANSI) and

ISO/IEC JTC 1/SC 22 ISO/IEC JTC 1/SC 22 Programming languages, their environments and system software interfaces is a standardization subcommittee of the Joint Technical Committee ISO/IEC JTC 1 of the International Organization for Standardization (ISO) and the Interna ...

/WG 14 of the

International Organization for Standardization The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Art ...

(ISO) and the

International Electrotechnical Commission The International Electrotechnical Commission (IEC; in French: ''Commission électrotechnique internationale'') is an international standards organization that prepares and publishes international standards for all electrical, electronic and ...

(IEC). Historically, the names referred specifically to the original and best-supported version of the standard (known as C89 or C90). Software developers writing in C are encouraged to conform to the standards, as doing so helps portability between compilers.

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 ISO is the most common abbreviation for the International Organization for Standardization. ISO or Iso may also refer to: Business and finance * Iso (supermarket), a chain of Danish supermarkets incorporated into the SuperBest chain in 2007 * Is ...

/ 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 A wide character is a computer character datatype that generally has a size greater than the traditional 8-bit character. The increased datatype size allows for the use of larger coded character sets. History During the 1960s, mainframe and min ...

'' support in the standard library, introducing and as well as multi-byte I/O * Addition of digraphs to the language * Specification of standard macros for the alternative specification of operators, e.g. and 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

#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199409L /* C95 compatible source code. */ #elif defined(__STDC__) /* C89 compatible source code. */ #endif

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 In computer science and computer programming, a data type (or simply type) is a set of possible values and a set of allowed operations on it. A data type tells the compiler or interpreter how the programmer intends to use the data. Most prog ...

: long long, _Bool, _Complex, and _Imaginary * Several new core language features, including static array indices, designated initializers, compound literals,

variable-length array In computer programming, a variable-length array (VLA), also called variable-sized or runtime-sized, is an array data structure whose length is determined at run time (instead of at compile time). In C, the VLA is said to have a variably modified t ...

flexible array member C struct data types may end with a flexible array member with no specified size: struct vectord ; Typically, such structures serve as the header in a larger, variable memory allocation: struct vectord *vector = malloc(...); vector->len = ...

variadic macro A variadic macro is a feature of some computer programming languages, especially the C preprocessor, whereby a macro may be declared to accept a varying number of arguments. Variable-argument macros were introduced in 1999 in the ''ISO/IEC 9899: ...

s, and

restrict 


In the C programming language, restrict is a keyword, introduced by the  C99 standard, that can be used in  pointer declarations. By adding this  type qualifier, a programmer hints to the compiler that for the lifetime of the pointer, no other po ...

keyword * Several new library headers, including stdint.h, <tgmath.h>, fenv.h, <complex.h> * Improved compatibility with several

C++ C, or c, is the third letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''cee'' (pronounced ), plural ''cees''. History "C" ...

features, including

inline function In the C and C++ programming languages, an inline function is one qualified with the keyword inline; this serves two purposes: # It serves as a compiler directive that suggests (but does not require) that the compiler substitute the body of t ...

s, single-line comments with //, mixing declarations and code, and universal character names in

identifiers An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, where the "object" or class may be an idea, physical countable object (or class thereof), or physical noncountable ...

* 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 Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, whic ...

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 Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object ...

for the

. C17 addresses defects in C11 without introducing new language features.

C2x

C2x C2x is an informal name for the next (after C17) major C language standard revision. It is expected to be voted on in 2023 and would therefore become C23. The most recent publicly available draft of C23 was released on January 24, 2023. The f ...

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 Decimal floating-point (DFP) arithmetic refers to both a representation and operations on decimal floating-point numbers. Working directly with decimal (base-10) fractions can avoid the rounding errors that otherwise typically occur when convert ...

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

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 Platform may refer to: Technology * Computing platform, a framework on which applications may be run * Platform game, a genre of video games * Car platform, a set of components shared by several vehicle models * Weapons platform, a system or ...

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 The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inst ...

libraries, or to the reliance on compiler- or platform-specific attributes such as the exact size of certain data types and byte

endianness In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most s ...

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. #if defined(__STDC__) && __STDC__ extern int getopt(int, char * const *, const char *); #else extern int getopt(); #endif In the above example, a prototype is used in a function declaration for ANSI compliant implementations, while an obsolescent non-prototype declaration is used otherwise. Those are still ANSI-compliant as of C99. Note how this code checks both definition and evaluation: this is because some implementations may set __STDC__ to zero to indicate non-ANSI compliance.

Compilers supporting ANSI C

* Amsterdam Compiler Kit (C K&R and C89/90) * ARM RealView *

Clang Clang is a compiler front end for the C, C++, Objective-C, and Objective-C++ programming languages, as well as the OpenMP, OpenCL, RenderScript, CUDA, and HIP frameworks. It acts as a drop-in replacement for the GNU Compiler Collection (GCC) ...

, using

LLVM LLVM is a set of compiler and toolchain technologies that can be used to develop a front end for any programming language and a back end for any instruction set architecture. LLVM is designed around a language-independent intermediate represe ...

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 *

LabWindows/CVI LabWindows/CVI (CVI is short for C for Virtual Instrumentation) is an ANSI C programming environment for test and measurement developed by National Instruments. The program was originally released as LabWindows for DOS in 1987, but was soon revis ...

* LCC * OpenWatcom (C89/90 and some C99) *

Microsoft Visual C++ Microsoft Visual C++ (MSVC) is a compiler for the C, C++ and C++/CX programming languages by Microsoft. MSVC is proprietary software; it was originally a standalone product but later became a part of Visual Studio and made available in both tr ...

(C89/90 and some C99) * Pelles C (C99 and C11. Windows only.)link to Pelles C pages
/ref> * vbcc (C89/90 and C99) *

Tiny C Compiler The Tiny C Compiler (a.k.a. TCC, tCc, or TinyCC) is an x86, X86-64 and ARM processor C compiler initially written by Fabrice Bellard. It is designed to work for slow computers with little disk space (e.g. on rescue disks). Windows operating syst ...

(C89/90 and some C99) * Oracle Developer Studio

References

External links

ISO C working group

''Draft ANSI C Standard'' (ANSI X3J11/88-090)
(May 13, 1988)
Third Public Review

''Draft ANSI C Rationale'' (ANSI X3J11/88-151)
(Nov 18, 1988)
''C Information Bulletin #1'' (ANSI X3J11/93-007)
(May 27, 1992)

*

* * {{DEFAULTSORT:Ansi C American National Standards Institute standards C (programming language) Programming language standards