Re: Returning a value to Perl from a C callback

[Kyle R. Burton]

On Tue, Aug 26, 2003 at 05:03:01PM -0400, Tao Wang wrote:
> I'm trying to write a C function that will return a scalar value. In
> between, the C function will call back to a Perl function to help it
> along. I have read that I shouldn't use Inline_Stack_Vars when calling
> back to Perl so I'm using the examples in perldoc percall instead. Here's
> a skeleton example of what I'm trying to do:

*snip*

> The exclaim subroutine just appends a "!" to a scalar. I figure when
> call_pv("exclaim", 0) is called, the return value of exclaim is now on the
> stack. How do I get this scalar to be returned to Perl (since I can't use
> Inline_Stack_Return(n) since Inline_Stack_Vars isn't being used)?
> 
> --Tao

You can return an SV* directly from your C functions, I've done that
often with good results.  Going with your example:

use strict;
use warnings;
use Inline C => 'DATA';

sub exclaim {
  my $string = shift;
  return "$string!";
}

my $s = call_exclaim("Hello");
print "s=$s\n";

exit 0;

__DATA__
__C__

SV*
call_exclaim( SV* string ) {
    SV *result;
    dSP;
    int count;

    ENTER;
    SAVETMPS;

    PUSHMARK(SP);
    XPUSHs(sv_2mortal(newSVsv(string)));
    PUTBACK;

    count = call_pv("exclaim", 0);

    SPAGAIN;

    if (count != 1) {
        croak("Big trouble\n");
    }

    result = POPs;
    SvREFCNT_inc(result);

    PUTBACK ;
    FREETMPS ;
    LEAVE ;

    return result;
}



Hope this helps,

Kyle R. Burton

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