I had something like this too but it doesn't work on Windows. Here is a stripped down example using Inline::C. On non-Windows (cygwin included), it outputs correctly: |ERROR| On Windows, it gives: || ERROR which shows you that the STDERR isn't being captured. 
use File::Temp qw(tempfile);
use Inline C;

open my $olderr, '>&STDERR'; # save STDERR
my ($fh, $fn) = tempfile();
open STDERR, '>&', $fh;

test_err();

open STDERR, '>&', $olderr; # reset STDERR
close $fh;

open my $e, '<', $fn;
my $err = <$e>;
print "|$err|\n";

__END__
__C__
void test_err()
{
(void)fprintf (stderr, "ERROR");
}

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In reply to Re^2: STDERR going to string by philkime
in thread STDERR going to string by philkime

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