Undefined variable $db_hostname - php

Question

I'm working with mysql and I'm trying to make a simple login to the database, but whenever I try to do it I get an error
Notice: Undefined variable: db_hostname in D:\xampp\htdocs\index.php on line 3
Notice: Undefined variable: db_username in D:\xampp\htdocs\index.php on line 3
Notice: Undefined variable: db_password in D:\xampp\htdocs\index.php on line 3
here is my code for the login.php
<?php//login.php
$db_hostname = 'localhost';
$db_database = 'publications';
$db_username = 'root';
$db_password = '';
?>
code for index.php
<?php
require_once('login.php') ;
$db_server = mysql_connect($db_hostname, $db_username, $db_password);
if(!$db_server) die ("Unable to connect to MySQL: " . mysql_error());
?>
I have no idea what I'm doing wrong.

Answer 1

change this (remove commented line or give space before it)
<?php//login.php
$db_hostname = 'localhost';
$db_database = 'publications';
$db_username = 'root';
$db_password = '';
?>
to,
<?php //login.php
$db_hostname = 'localhost';
$db_database = 'publications';
$db_username = 'root';
$db_password = '';
?>

Answer 2

In PHP the <?php directive must be followed by whitespace, newline, or EOF (the file ends after the directive).
You normally get a fatal error and your script stops.
However you're using an outdated and unsupported version of PHP which just passes your "to be" PHP code directly to stdout. This can have security implications, like in your case, you've published the database credentials (if any).