(gcc.info.gz) Alternate Keywords

 
 5.41 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').  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', 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.

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