#include <stdlib.h>

int* f1() {
  int   x = 37;
  int * p = &x;
  return p;
}

int** f2() {
  int *  p = f1();
  int ** q = NULL;
  *p = 1234567; // dangling-pointer dereference (what if q is there)!
  return q; // not dangling (just returning NULL)
}

void f3() {
  int * p1 = calloc(1,sizeof(int));
  int * p2 = calloc(1,sizeof(int));
  int * p3 = calloc(1,sizeof(int));
  int * q1 = p1;
  int * q2 = p2;
  free(p1);
  *p1 = 38; // dangling-pointer dereference
  *q1 = 38; // dangling-pointer dereference
  free(p2);
  free(p2); // double-free
  free(q2); // triple-free
  return; // space-leak: *p3 will exist until program exit
}