Steve Hay <[EMAIL PROTECTED]> writes:
>Why is it that when I create an SV and assign magic to it in an XSUB,
>and then return the magical SV to Perl code, I find that the scalar in
>the Perl code no longer seems to have magic?
If you print something the FooFree() you will see what is happening.
You return an SV.
SV gets copied to $a - magic isn't copied
Your SV gets free-d
$a is passed to your function.
Normally this doesn't matter as "objects" return references
to the thing which has magic.
>
>The attached sample module has XSUB's to create a magical SV (fooalloc
>and fooallocext), an XSUB to use the magical SV created (foo) and
>another to free it (foofree, not strictly necessary since the SV here is
>mortal anyway).
>
>I was intending that when I run
>
>perl -Mblib -MFoo -e "$a=Foo::fooalloc();Foo::foo($a);Foo::foofree($a)"
>
>it would print "Hello, world.".
>
>But it doesn't. It croak()'s in foo() claiming that it can't find the
>magic on the SV passed in.
Because $a hasn't got any.
You could make it work if you passed in the SV:
Foo::fooalloc($a)
And I think
Foo::foo(Foo::fooalloc())
will work.
>
>I've added some sv_dump()'s into the allocators to look at the SV being
>returned; using Devel::Peek::Dump() in the Perl code I can also look at
>what it received, and I find that they're completely different:
>
>perl -Mblib -MFoo -MDevel::Peek -e "$a=Foo::fooalloc();Dump($a)"
>
>outputs this:
>
>SV = PVMG(0x1835170) at 0x1820184
^^^^^^^^^ - Your SV
> REFCNT = 1
> FLAGS = (TEMP,RMG)
> IV = 0
> NV = 0
> PV = 0
> MAGIC = 0x182a188
> MG_VIRTUAL = 0x354410
> MG_TYPE = PERL_MAGIC_ext(~)
> MG_PTR = 0x185a738 ""
The dump of the temporary (mortal) you return.
>SV = PVMG(0x1835190) at 0x183578c
^^^^^^^^^ - SV for $a
> REFCNT = 1
> FLAGS = ()
> IV = 0
> NV = 0
> PV = 0
The dump of SV for $a.
>
>void
>foofree(sv)
> SV *sv;
>PPCODE:
>{
> SvREFCNT_dec(sv);
>}
Not a good idea - the SV isn't yours.
