The following Inline::CPP script seems to do what you need on perl-5.8.8 (but not on perl-5.10.0):

use warnings;
use Inline CPP => Config =>
    BUILD_NOISY => 1;

use Inline CPP => <<'EOC';

void add_nir(int x, int y, AV * perlList) {
    SV* perlItem=newSViv(2);
    av_push(perlList, perlItem);
}

EOC

my @test = (1, 2);
print "@test\n";
my $reftest = \@test;
add_nir(1, 4, $reftest);
print "@test\n";
[download]

On perl-5.8.8 that correctly outputs:

1 2
1 2 2
[download]

and you can see that the "2" was, in fact, pushed onto the array. But, on perl-5.10.0 I get Can't locate auto/main/add_nir.al in @INC ... which is similar to what you are getting. Apparently, one can't supply an AV* arg to an Inline::CPP function on perl-5.10.0, though there's no such problem with perl-5.8.8. I don't know whether this is an Inline::CPP bug or a perl bug - probably Inline::CPP.

The above script also works fine on perl-5.10.0 as an Inline::C script - do you really need to use Inline::CPP ? (There's a useful example of doing object-oriented inline using Inline::C in 'perldoc Inline::C-Cookbook'. Look for "Soldier".)

If you really do need Inline::CPP, you're in luck - there's a simple rewrite of the above script that has add_nir() take an SV instead of an AV, and it works fine with Inline::CPP on perl-5.10.0:

use warnings;
use Inline CPP => Config =>
    BUILD_NOISY => 1;

use Inline CPP => <<'EOC';

void add_nir(int x, int y, SV * perlList) {
    SV* perlItem=newSViv(2);
    av_push((AV*)SvRV(perlList), perlItem);
}


EOC

my @test = (1, 2);
print "@test\n";
my $reftest = \@test;
add_nir(1, 4, $reftest);
print "@test\n";
[download]

At least that works fine for me on perl-5.10.0. Note that the perl code is exactly the same as in the first script. The only difference is in the way the add_nir() function has been constructed.

Cheers,
Rob