PHP AutoLoad Magic Method, this is for pre SPL implementations

phpautoloader.php

<?php

function __autoload ($class_name)
{
  if (!class_exists($class_name, false)) {
    $class_file_path = str_replace('_', '/', $class_name) . '.php';
    require($class_file_path);
  }
}

/*or*/

function __autoload($class_name) 
{
    $filename = str_replace('_', DIRECTORY_SEPARATOR, strtolower($class_name)) . '.php';

    $file = $filename; //Concat filename with defined app root

    if (!file_exists($file))
    {
        return FALSE;
    }
    include($file);
}