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.

[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] 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 

It's better to use "#if __STDC__" as above rather than "#ifdef __STDC__" because some implementation may set __STDC__ to zero to indicate non-ANSI compliance. "#if" will treat any identifiers that couldn't be replaced by a macro as zero (0). Thus even if the macro "__STDC__" is not defined to signify non-ANSI compliance, "#if" will work as shown.

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 and C90, but their use is discouraged.

[edit] Compilers supporting ANSI C

• GCC
• Microsoft Visual C++ (C90. A few features of C99)
• ARM RealView

[edit] See also

• C++
• SystemC

[edit] 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)
• Schreiner, Axel-Tobias (Hanser). Object oriented programming with ANSI-C. Hanser. ISBN 3-446-17426-5. http://hdl.handle.net/1850/8544. 
• "ISO/IEC 9899:1999 Programming Languages -- C". American National Standards Institute. http://webstore.ansi.org/RecordDetail.aspx?sku=ISO%2FIEC+9899%3A1999. 

• "ANSI Standards Action Vol. 36, #48". American National Standards Institute. 2005-12-02. http://publicaa.ansi.org/sites/apdl/Documents/Standards%20Action/2005%20PDFs/SAV3648.pdf. 

[edit] References