Predefined Macros in gcc

gcc (well cpp, the preprocessor) provides several predefined macros. Many of these are platform independent, for instance __FILE__ and __LINE__. Others are platform dependent (or "system-specific" as the gcc manual puts it). So how do you know what your particular platform defines? Try this:
cpp -dM /dev/null I stumbled across this trick the other day on Apple's mailing lists archives.