The GNU C library is compatible with the C standard adopted by the
American National Standards Institute (ANSI):
American National Standard X3.159-1989—“ANSI C” and later
by the International Standardization Organization (ISO):
ISO/IEC 9899:1990, “Programming languages—C”.
We here refer to the standard as ISO C since this is the more
general standard in respect of ratification.
The header files and library facilities that make up the GNU library are
a superset of those specified by the ISO C standard.
If you are concerned about strict adherence to the ISO C standard, you
should use the `-ansi' option when you compile your programs with
the GNU C compiler. This tells the compiler to define only ISO
standard features from the library header files, unless you explicitly
ask for additional features. See Feature Test Macros, for
information on how to do this.
Being able to restrict the library to include only ISO C features is
important because ISO C puts limitations on what names can be defined
by the library implementation, and the GNU extensions don't fit these
limitations. See Reserved Names, for more information about these
This manual does not attempt to give you complete details on the
differences between ISO C and older dialects. It gives advice on how
to write programs to work portably under multiple C dialects, but does
not aim for completeness.
Published under the terms of the GNU General Public License