1  extern void abort (void);
       2  
       3  struct delay_block {
       4    struct delay_block *succ;
       5  };
       6  
       7  static struct delay_block Timer_Queue;
       8  
       9  struct delay_block* time_enqueue (struct delay_block *d)
      10  {
      11    struct delay_block *q = Timer_Queue.succ; 
      12    d->succ =  (void *)0;
      13    return Timer_Queue.succ;
      14  }
      15  
      16  int main(void)
      17  {
      18    Timer_Queue.succ = &Timer_Queue;
      19    if (time_enqueue (&Timer_Queue) != (void*)0)
      20      abort ();
      21    return 0;
      22  }
      23