1  typedef void* Ptr;
       2  
       3  struct A
       4  {
       5    int i;
       6    union
       7    {
       8      Ptr p;
       9      char *q;
      10    } u;
      11  };
      12  
      13  static void foo(struct A *p, char *q)
      14  {
      15    if (p->i)
      16      p->u.p = 0;
      17    else
      18      p->u.q = q;
      19  }
      20  
      21  void bar(struct A *p, char *q)
      22  {
      23    foo(p, q);
      24  }