ISO C

ANSI C, ISO C and Standard C refer to the successive standards for the C programming language published by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). 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 aids portability between compilers.

The first standard for C was published by ANSI. Although this document was subsequently adopted by International Organization for Standardization (ISO) and subsequent revisions published by ISO have been adopted by ANSI, the name ANSI C (rather than ISO C) is still more widely used. While some software developers use the term ISO C, others are standards body–neutral and use Standard C.

In 1983, the American National Standards Institute formed a committee, X3J11, to establish a standard specification of C. The 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 C99 but using the same labelling method.

The same standard as C89 was ratified by the International Organization for Standardization 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This standard has been withdrawn by both ANSI/INCITS and ISO/IEC.

In 1995, the ISO published an extension, called Amendment 1, for the ANSI-C standard. Its full name finally was ISO/IEC 9899/AMD1:1995 or nicknamed C95. Aside from error correction there were further changes to the language capabilities, such as:

In addition to the amendment, two technical corrigenda were published by ISO for C90:

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:

Three technical corrigenda were published by ISO for C99:

This standard has been withdrawn by both ANSI/INCITS and ISO/IEC in favour of C11.

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