foo *
routine(a, b, c=NULL)
 char *a;
 int b;
 bar_t * c;

 CODE:
  RETVAL = croutine( a, b, (c && SvOK(ST(2)) ) ?
    c : cdefault );
 OUTPUT: RETVAL


##</code><code>##

 my $c = $objref;
 routine( $a, $b, $c);

##</code><code>##

 routine( $a, $b);

##</code><code>##

  my $c;
  $c = $objref if( false );
  routine( $a, $b, $c );