I tried and indeed got results you described.

But given "my version" behaves as it should be. Please explain why it is not.

You need concatenation SV subroutine - you get it. You receive 'undefined' warning when SV is indeed undefined, this warning could perfectly avoided, but chunk of code do what it is asked to. 

#! perl -slw
use strict;

use Inline C => << '__C__', NAME => 'test', CLEAN_AFTER_BUILD => 0;
#include <stdio.h>

SV* test( SV *a, SV *b ) {
    SV *c = newSVsv(a);
    sv_catsv(c,b);
    return c;
}
__C__

print test( 'bill', 'fred' );

my( $p, $q ) = ( 'fred' );
print test( $q, $p );

$q = 'bill';
print test( $q, $p );

$q = 1;
print test( $q, $p );

$p = 1;
print test( $q, $p );

[download]
Right now, all is behaving, even w/o refcnt mess.
Or do you want inplace editing of scalar? Then you need to pass a reference to SV and in the very beginning of subroutine dereference it once!

BR,
Vadim.

In reply to Re^3: XS/Inline::C concat *any* two SVs. by vkon
in thread XS/Inline::C concat *any* two SVs. by BrowserUk

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