#include <stdio.h>

#define swap(a, b) swap_( (void **) &(a), (void **) &(b) )
void swap_(void** a, void** b)
{
    void* temp = *a;
    *a = *b;
    *b = temp;
}

int main(void)
{
    int a = 5, b = 10;
    printf("%d %d\n", a, b);
    swap(a, b);
    printf("%d %d\n", a, b);
    return 0;
}