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5.38 Alternate Keywords
‘-ansi’ and the various ‘-std’ options disable certain
keywords. This causes trouble when you want to use GNU C extensions, or
a general-purpose header file that should be usable by all programs,
including ISO C programs. The keywords
inline are not available in programs compiled with
‘-ansi’ or ‘-std’ (although
inline can be used in a
program compiled with ‘-std=c99’). The ISO C99 keyword
restrict is only available when ‘-std=gnu99’ (which will
eventually be the default) or ‘-std=c99’ (or the equivalent
‘-std=iso9899:1999’) is used.
The way to solve these problems is to put ‘__’ at the beginning and
end of each problematical keyword. For example, use
__inline__ instead of
Other C compilers won't accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords. It looks like this:
#ifndef __GNUC__ #define __asm__ asm #endif
‘-pedantic’ and other options cause warnings for many GNU C extensions.
prevent such warnings within one expression by writing
__extension__ before the expression.
__extension__ has no
effect aside from this.