$config_dbname = "erbil";
$config_dbuser = "root";
$config_dbpassword = "";
$config_dbprefix ="erbil_";
$config_dbserver = "localhost";

<?php

include_once dirname(__FILE__).'/mysql.class.php';

$sql = new MySQL();

$sql->connect($config_dbuser, $config_dbpassword, $config_dbserver);

$sql->selectdb($config_dbname, $config_dbprefix);

?>

 <?php
$servername = "localhost";
$username = "username";
$password = "password";

try {
    $conn = new PDO("mysql:host=$servername;dbname=myDB", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Connected successfully";
    }
catch(PDOException $e)
    {
    echo "Connection failed: " . $e->getMessage();
    }
?> 

$sql->selectdb($config_dbname, $config_dbprefix);