xs and references

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi, monks!
I want to write on XS something like this:

sub testSub
{
    my $test_var = shift;

    $$test_var = "Hello!;)\n";

    return 1;
}
[download]

I'v tried to use following way:

int
testSub(const char** test_var)
    CODE:
    ...
[download]

But it does not works =\

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Re: xs and references by chromatic (Archbishop) on Feb 27, 2009 at 17:53 UTC
It doesn't work because Perl is not C. Scalars in Perl are SVs (and Perl strings are PVs, not chars). Also Perl passes and returns values on a stack (not the C stack), not through C's calling conventions. Read perlxstut to understand how passing and receiving parameters work. Then browse perlapi for specific functions. I believe (without reading it myself this morning) you need to check that you have a valid RV (something like `SvRVOK`) -- which represents a reference in Perl -- then access the referent and assign its PV (potentially upgrading it to contain a PV).	[reply] [d/l]
Re: xs and references by syphilis (Archbishop) on Feb 28, 2009 at 06:53 UTC
As a starter: `use warnings; use Inline C => Config => CLEAN_AFTER_BUILD => 0, BUILD_NOISY => 1; use Inline C => <<'EOC'; int testSub(SV * x) { if(!SvROK(x)) croak ("Not a reference"); sv_setpv(SvRV(x), "Hello!;)\n\0"); return 1; } EOC $init = "barbarella"; $test_var = \$init; testSub($test_var); print "$$test_var\n$init\n";` [download] For me, that outputs: `Hello!;) Hello!;)` [download] If you specifically need to see the XS file that Inline::C autogenerated for this particular exercise, you'll find it in the build directory (./_Inline/build). Cheers, Rob	[reply] [d/l] [select]
Re^2: xs and references by Anonymous Monk on Mar 02, 2009 at 07:57 UTC
thanks to all!)	[reply]
Re: xs and references by Anonymous Monk on Feb 27, 2009 at 13:17 UTC
of course it doesn't work , its incomplete :) Try useing sv_setpv.	[reply]