I am getting the folllowing error E:\xampp\htdocs\ecommerce\index.php(2): require_once('E:\\xampp\\htdocs...')

in index.php, my code is

  require_once ("include/initialize.php");

and in ititialize.php, my code is

   defined('DS') ? null : define('DS', DIRECTORY_SEPARATOR);
   defined('SITE_ROOT') ? null : define ('SITE_ROOT', $_SERVER['DOCUMENT_ROOT'].DS.'ecommerce');
   defined('LIB_PATH') ? null : define ('LIB_PATH',SITE_ROOT.DS.'include');