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 asm
, typeof
and
inline
are not available in programs compiled with
-ansi
or -std
(although inline
can be used in a
program compiled with -std=c99
or a later standard). 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
), or an option for a later standard
version, is used.
The way to solve these problems is to put __
at the beginning and
end of each problematical keyword. For example, use __asm__
instead of asm
, and __inline__
instead of inline
.
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.
You can
prevent such warnings within one expression by writing
__extension__
before the expression. __extension__
has no
effect aside from this.