Useful C Macros

Let's share the macros we use that make our C code really EXPERT!!

Right now I'm specifically interested in macros to add half-assed object orientation. Thanks!!

I'll contribute myself:
#define mainstart int main(int argc, char **argv) {

>>18
What kind of assumptions did the compiler make use of? I see their 'default unreachable' example, and I assume you can assume lack of pointer aliasing and the like.