Node: Alternate Keywords, Next: , Previous: Explicit Reg Vars, Up: C Extensions

Alternate Keywords

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

-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.