Alternate Keywords (Using the GNU Compiler Collection (GCC)) (original) (raw)

6.48 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 andinline 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 keywordrestrict 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.