Why do I get "Warning: require_once(config): failed to open stream: No such file or directory" when trying to run this code?

I'm currently working on programming my very own online store with NetBeans IDE 8.0.2 using PHP. My system is Windows 7 32bit and my localhost is powered by WampServer 2.5. I'm following THC Courses: https://www.youtube.com/playlist?list=PLbXVpMmmrntAvOYgkqhHW0hVu8dWUNyfz

So far everything was going great but I got stock at this video: S2 {Building Framework} Class and method (p6). The guy is asking to echo a sample text on the screen to test the code, but I get these two error messages when running the project on localhost:

Warning: require_once(config): failed to open stream: No such file or directory in C:\wamp\www\ecommerce\inc\autoload.php on line 2
Fatal error: require_once(): Failed opening required 'config' (include_path='.;C:\php\pear') in C:\wamp\www\ecommerce\inc\autoload.php on line 2

autoload.php:

<?php

    require_once('config');

    function __autoload($class_name) {

        $class = explode("_", $class_name);
        $path = implode("/", $class).".php";
        require_once($path);

    }

Core.php:

<?php

    class Core {

        public function run() {
            echo "Hello this is a print test";

        }

    }

index.php:

<?php

    require_once'inc/autoload.php';
    $core = new Core();
    $core->run();

config.php:

<?php

    if(!isset($_SESSION)) {
        session_start();

    }

    //site domain name with http
    defined("SITE_URL")
    ||define("SITE_URL", "http://".$_SERVER['SERVER_NAME']);

    //directory seperator
    defined("DS")
    ||define("DS", DIRECTORY_SEPERATOR);

    //root path
    defined("ROOT_PATH")
    ||define("ROOT_PATH", realpath(dirname(__FILE__) .DS.".." .DS));


    //classes folder
    defined("CLASSES_DIR")
    ||define("CLASSES_DIR", classes);

    //pages folder
    defined("PAGES_DIR")
    ||define("PAGES_DIR", pages);



    //modules folder
    defined("MOD_DIR")
    ||define("MOD_DIR", "mod");


    //inc folder
    defined("INC_DIR")
    ||define("INC_DIR", "inc");


    //templates folder
    defined("TEMPLATE_DIR")
    ||define("TEMPLATE_DIR", "template");

    //emails path
    defined("EMAILS_PATH")
    ||define("EMAILS_PATH", ROOTH_PATH.DS. "emails");

    //catalogue images path
    defined("CATALOGUE_PATH")
    ||define("CATALOGUE_PATH", ROOTH_PATH.DS. "media" .DS."catalogue");


    //add all above directories to the include path
    set_include_path(implode(PATH_SEPERATOR, array(
    realpath(ROOTH_PATH.DS.CLASSES_DIR),
    realpath(ROOTH_PATH.DS.PAGES_DIR),
    realpath(ROOTH_PATH.DS.MOD_DIR),
    realpath(ROOTH_PATH.DS.INC_DIR),
    realpath(ROOTH_PATH.DS.TEMPLATE_DIR).
    get_include_path()

    )));

Solution

Change this:

require_once('config');

to:

require_once('config.php');
                   //^^^See here file extension

(Also make sure it's in the same directory with autoload.php, otherwise change the path)

EDIT:

Or try i with a absolute path like this:

require_once(dirname(__FILE__) . "/config.php");

EDIT 2:

Since you now get error messages from the config file, means that it got included, but still has some errors in it!

The first would be this:

//directory seperator
defined("DS")
||define("DS", DIRECTORY_SEPERATOR);
             //^^^^^^^^^^^^^^^^^^^ Typo must be: DIRECTORY_SEPARATOR

Next one is here:

//classes folder
defined("CLASSES_DIR")
||define("CLASSES_DIR", classes);
                      //^^^^^^^ This isn't a constant so if it is a string put quotes around it

Same error here:

//pages folder
defined("PAGES_DIR")
||define("PAGES_DIR", pages);
                    //^^^^^

Next error here:

//emails path
defined("EMAILS_PATH")
||define("EMAILS_PATH", ROOTH_PATH . DS .  "emails");
                      //^^^^^^^^^^ Typo must be: ROOT_PATH , you have one h too much

Same here:

//catalogue images path
defined("CATALOGUE_PATH")
||define("CATALOGUE_PATH", ROOTH_PATH.DS. "media" .DS."catalogue");
                         //^^^^^^^^^^

And all over the palce you have 6 typos here:

//add all above directories to the include path
set_include_path(implode(PATH_SEPERATOR, array(
                       //^^^^^^^^^^^^^^ Typo must be: PATH_SEPARATOR 
realpath(ROOTH_PATH.DS.CLASSES_DIR),
       //^^^^^^^^^^ Typo must be: ROOT_PATH , you have one h too much
realpath(ROOTH_PATH.DS.PAGES_DIR),
       //^^^^^^^^^^
realpath(ROOTH_PATH.DS.MOD_DIR),
       //^^^^^^^^^^
realpath(ROOTH_PATH.DS.INC_DIR),
       //^^^^^^^^^^
realpath(ROOTH_PATH.DS.TEMPLATE_DIR).
       //^^^^^^^^^^
get_include_path()

)));

EDIT 3:

Here you can simplify these 2 lines and i would change the require, so it works even if you include the file itself into another one! Like this:

autoload.php:

function __autoload($class_name) {

    $class = explode("_", $class_name);
    $path = implode("/", $class).".php";
    require_once($path);

}

to this:

function __autoload($class_name) {

    $path = str_replace("_", "/", $class_name) . ".php";
    require_once(dirname(__FILE__) . "/" . $path);

}