A file is included in PHP, but the variable is Undefined

I am new to PHP and I started using XAMPP to build the site. I have the code below

db.php:

<?php
    $hostName='localhost';
    $userName='xxxxxxxxx';
    $userPass='xxxxxxxxx';
?>

and test.php:

<?php
    include 'db.php';
    echo $hostName;
?>

but now it shows me Note: Undefined variable: hostName

I found that register_globals needs to be set to "on" in php.ini, but after I installed it, XAMPP show: The 'register_globals' directive is no longer available in PHP when I restart XAMPP.

I am moving the same code in Hosting24, but it works, who can help?