1  typedef struct
       2  {
       3    void *p;
       4  } Ptr;
       5  
       6  struct A
       7  {
       8    int i;
       9    union
      10    {
      11      Ptr p;
      12      char *q;
      13    } u;
      14  };
      15  
      16  extern Ptr get_stuff (void);
      17  extern void use_stuff (char *);
      18  
      19  static void foo(struct A p, char *q)
      20  {
      21    if (p.i)
      22      p.u.p = get_stuff ();
      23    else
      24      p.u.q = q;
      25  
      26    use_stuff (p.u.q);
      27  }
      28  
      29  void bar(struct A *p, char *q)
      30  {
      31    foo(*p, q);
      32  }