#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
int main (int argc, char *argv[])
{
    double a = 1.1;
    double b = 2.2;
    void * A = (void *) &a;
    void * B = (void *) &b;
    ptrdiff_t s = (A - B);
    printf ("differenza: %i\n", s);
    return 0;
}

differenza: 8