I have an XS routine that (simplified) looks like this: 
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

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From perl, we can say 
 my $c = $objref;
 routine( $a, $b, $c);

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or 
 routine( $a, $b);

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BUT, if we say: 
  my $c;
  $c = $objref if( false );
  routine( $a, $b, $c );

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We fail with "c is not a reference" at runtime, when the interface code sees that c is not a reference.

This is because $c contains undef. But I'm prepared to supply another value in this case. (Note the SvOK(ST(2))).

How do I tell XS that a reference OR undef is OK for a parameter (c)?

Many thanks,

This communication may not represent my employer's views, if any, on the matters discussed.

In reply to XS: How to enable passing ref or undef? by tlhackque

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