Implement generic swap macro in C

Possible Duplicate:
is there an equivalent of std::swap() in c

Hi folks,

I was attempting a problem to write a generic swap macro in C and my macro looks like this:

#define swap(x,y) { x = x + y; y = x - y; x = x - y; }

It works fine for integers and floats but I am unsure if there is any catch in it. What if by generic macro they mean swapping pointers, characters etc ? Can anyone help me with writing a generic macro for swapping every input ?

Thanks