How to Create xml file for php connection string

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PHP

<?php

$iterations = 3;
$hash = crypt($password,$salt);
for ($i = 0; $i < $iterations; ++$i)
{
    $hash = crypt($hash . $password,$salt);
	echo $hash;
}


?>

I am new gradual with less experience in Developing web appli cation.
Am a building a very sensitive application in php and Mysql database server as the back end.
But in my login page in particular and any page in my application i use the connection string to my database server directly in my code. No doubt this is a security hole.
In ASP.NET The webconfig is use, i want to create and xml file to save my connection string there i would be reading it from my application.
I did enough google to no vail. pls show me a sample.
The code above is my Authentication.php but i don't want to code the connection string to db directly. Just to reff.
Thanks