| Alternate Keywords

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'-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.