and the various
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
are not available in programs compiled with
can be used in a program compiled with
). The ISO C99 keyword
is only available when
(which will eventually be the default) or
(or the equivalent
), 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
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
and other options cause warnings for many GNU C extensions. You can prevent such warnings within one expression by writing
before the expression.
has no effect aside from this.