*****Listing 3*****

     void someproc(p)
         something * p;
         {
     #if DEBUG
          if(!p)
             {
              if(report_null_pointer("someproc: p"))
                  return;
             }
     #endif
          }

and use a target procedure which consists of

     short report_null_pointer(where)
        char * where;
        {
         fprintf(stderr,"NULL POINTER: %s\n",where);
         return stop(where);
        }

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