1extern void abort(void); 2void foo(int *p) 3{ 4 int x; 5 int y; 6 x = *p; 7 *p = 0; 8 y = *p; 9 if (x != y) 10 return; 11 abort (); 12} 13 14int main() 15{ 16 int a = 1; 17 foo(&a); 18 return 0; 19} 20