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");
}