ANSI C

In 1989 the American National Standards Institute (ANSI) finished development and ratified standard ANSI X3.159-1989 “Programming Language C”. This version of the language is typically referred to as ANSI C, Standard C or sometimes C89. In 1989 the same standard with minor changes was accepted by International Organization for Standardization as ISO/IEC 9899:1990.

The standardization process aimed to create a superset of K&R C which would include language features added after the book was published. Besides, the standard included several new features such as function prototypes, void pointers, localization support and preprocessor improvements.

To write code which depends on features which differ in ANSI C and earlier standards, use __STDC__ macro.

ANSI C is supported by most modern compilers, and almost all code written lately conforms to it. However, most programs are written so that they can be compiled only by one or several compilers, due to using non-standard libraries or some compiler-dependent features.