use Win32::API;
my $dec = Win32::API->new('mydll.dll', 'OpenConnection', 'PPP', 'L') or die $^E;
$strDatabase = "test";
$strLoginUser = "test";
$strLoginPwd = "test";
# converting to C String
$db = pack('a*x', $strDatabase);
$user = pack('a*x', $strLoginUser);
$pwd = pack('a*x', $strLoginPwd); 

$return = $dec->Call($db, $user, $pwd);
print $return;