The option -traditional
disables certain keywords;
-ansi
and the various -std
options disable certain
others. This causes trouble when you want to use GNU C extensions, or
ISO C features, in a general-purpose header file that should be usable
by all programs, including ISO C programs and traditional ones. The
keywords asm
, typeof
and inline
cannot be used
since they won't work in a program compiled with -ansi
(although inline
can be used in a program compiled with
-std=c99
), while the keywords const
, volatile
,
signed
, typeof
and inline
won't work in a program
compiled with -traditional
. 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 __asm__
instead of asm
, __const__
instead of const
, 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.