also you can define them.. which is usually how i like to do it. which is secure, again, as long as there is no output in the file.
define('DB_HOST', 'hostname');
define('DB_USER', 'username');
define('DB_PASS', 'password');
define('DB_NAME', 'database');
mysql_connect(DB_HOST, DB_USER, DB_PASS);
mysql_select_db(DB_NAME);