-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 -std=c11
). 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.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-5.4.0/gcc/Alternate-Keywords.html