This is a swap macro in c, and can swap arbitrary types.

swap.c

#include <string.h>

#define swap(x, y) do \                                                        
    { unsigned  char swap_temp[sizeof(x) == sizeof(y) ? (signed)sizeof(x):-1];\
        memcpy(swap_temp, &y, sizeof(x));  \
        memcpy(&y, &x,        sizeof(x));  \
        memcpy(&x, swap_temp, sizeof(x));  \
    } while(0)
// this snippet from stackoverflow
// http://stackoverflow.com/questions/3982348/implement-generic-swap-macro-in-c