ANSI C
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ANSI C is the standard published by the American National Standards Institute (ANSI) for the C programming language. Software developers writing in C are encouraged to conform to the requirements in the document, as it encourages easily portable code.
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[edit] History of ANSI C and ISO C
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.
[edit] C89
In 1983, the American National Standards Institute formed a committee, X3J11, to establish a standard specification of C. After a long and arduous process, 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", or sometimes "C89" (to distinguish it from C99).
[edit] C90
In 1990, the ANSI C standard (with a few minor modifications) was adopted by the International Organization for Standardization as ISO/IEC 9899:1990. This version is sometimes called C90. Therefore, the terms "C89" and "C90" refer to essentially the same language.
[edit] C99
In March 2000, ANSI adopted the ISO/IEC 9899:1999 standard. This standard is commonly referred to as C99, and it is the current standard for C programming language.
[edit] Aims
One of the aims of the ANSI C standardization process was to produce a superset of K&R C (the first published standard), incorporating many of the unofficial features subsequently introduced. However, the standards committee also included several new features, such as function prototypes (borrowed from the C++ programming language), and a more capable preprocessor. The syntax for parameter declarations was also changed to reflect the C++ style.
[edit] Support from major compilers
ANSI C is now supported by almost all the widely used compilers. Most of the C code being written nowadays is based on ANSI C. Any program 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.
[edit] Compliance detectability
To mitigate the differences between K&R C and the ANSI C standard, the __STDC__ macro can be used to split code into ANSI and K&R sections.
#if __STDC__ extern int getopt(int, char * const *, const char *); #else extern int getopt(); #endif
Some suggest using "#if __STDC__" as above rather than "#ifdef __STDC__" because some compilers set __STDC__ to zero to indicate non-ANSI compliance.
