Warning: mysql_connect(): Unknown MySQL server host 'DB_HOST' (1)

Hello guys,

I am trying to run a script but it could not get connected to mysql and I have tried it on 2 different free hosts with different versions of php. I get this error:

Warning: mysql_connect(): Unknown MySQL server host 'DB_HOST' (1) in /home/u947202749/public_html/inc/functions.php on line 1918 Couldn't make connection.

Here is my function file with line 1917 to 1921

 function connect(){
        $link = mysql_connect(DB_HOST, DB_USER, DB_PASS) or die("Couldn't make connection.");
        $db = mysql_select_db(DB_NAME, $link) or die("Couldn't select database");
        return $db;
    }

and here is my configuration file which is 100% accurately set according to right details but I wont share them here due to security reasons.

$site_url = "http://toorhamza12.fun2pk.com";
$site_name = "Image Hosting";
$site_title = "Image Hosting Script";
$site_meta_description = "Share your images";
$site_meta_keywords = "images, share";
$site_meta_author = "Zamfi";
$site_version = "1.2";
$logo_location = "css/img/logo.png";

// ADMIN CONFIGURATIONS
define("ADMIN_EMAIL", "admin@yoursite.com"); // email address for various notifications like IPN's confirmations or error logs, contact form and other administrative things.
define("UPLOAD_ONLY_REGISTERED", 0); // 1 = UPLOAD ONLY FOR REGISTERED USERS // 0 = UPLOAD FOR EVERYBODY

// DATABASE CONFIGURATIONS
define ("hidden", ""); // set database host
define ("hidden", ""); // set database user
define ("hidden",""); // set database password
define ("hidden",""); // set database name

and so on. Please help me regarding this issue. Thank You.