What will happened if you are tring to connect with mysql db without hostname, username and password

I surprised by doing this, i just written code for mysql connectivity from php script by without specifying HOSTNAME, USERNAME AND PASSWORD.

The below is the code which was written by me.

<?php
 $con=mysql_connect("","","");
 if($con)
     echo connected;
 else {
     echo not;
}
?>

After executing this program from web browser it's showing connected.

Note:
 If your not specifying the hostname, username and password. it will shows connected message..