Q:

How to debug "Call to undefined function session_register()" in PHP? 

I have created a basic login in using php.  I have fixed my previous error thanks to your help however I am now receiving a new error on line 36:

Call to undefined function session_register() in /Applications/XAMPP/xamppfiles/htdocs/game development/checklogin.php on line 36

I'm not sure why.  Any ideas on how to fix this? 
    <? php

            ob_start();
            $host="localhost"; // Host Name 

            $username="root"; // Mysql Username

            $password=""; // Mysql Password 

            $db_name="DylansDB"; // Database Name 

            $tbl_name="members";

            // Connect to server and select databse. 
            mysql_connect("$host", "$username", "$password")or die("cannot connect"); 
            mysql_select_db("$db_name")or die("cannot select DB");

            // Define $myusername and $mypassword 
            $myusername=$_POST['myusername']; 
            $mypassword=$_POST['mypassword']; 

            // To protect MySQL injection
            $myusername = stripslashes($myusername);
            $mypassword = stripslashes($mypassword);
            $myusername = mysql_real_escape_string($myusername);
            $mypassword = mysql_real_escape_string($mypassword);
            $sql="SELECT * FROM $tbl_name WHERE username='$myusername' and password='$mypassword'";
            $result=mysql_query($sql);

            // Mysql_num_row is counting table row
            $count=mysql_num_rows($result);

            // If result matched $myusername and $mypassword, table row must be 1 row
            if($count==1){

            // Register $myusername, $mypassword and redirect to file "login_success.php"
            session_register("myusername");
            session_register("mypassword"); 
            header("location:login_success.php");
            }
            else {
            echo "Wrong Username or Password";
            }
            ob_end_flush();
   ? >

A:

$host="localhost"; // Host Name 

$username="root"; // Mysql Username

 $password=""; // Mysql Password 

 $db_name="DylansDB"; // Database Name 

  $tbl_name="members"; // Table Name

