1  #include <stdio.h>
       2  
       3  #pragma weak undef_func
       4  
       5  extern int undef_func (void);
       6  int (*ptr_to_func)(void) = undef_func;
       7  
       8  int
       9  main (void)
      10  {
      11    if (ptr_to_func == NULL)
      12      printf ("PASSED\n");
      13  
      14    return 0;
      15  }