__autoload不运行？

Question

I have a file structure that looks like this;

/
/public
  -index.php
  -login.php
/config.php
/init.php
/classes/ClassGroup/ClassName.class.php

__autoload is defined in config.php, with absolute path to classes. config.php is required in index.php, but when I try to initiate a new class;

$user = new User_User;

Results in;

Fatal error: Class 'User_User' not found in /......./public/index.php on line 27

It does not find it, and when trying to echo out something at the very start of __autoload(), it doesnt do that either, so it seems to me that it does not run the function when not finding a class. Anyone have a clue what the problem might be?

function __autoload($class){
    //echo "autoloader started";
    $pieces = explode('_', $class);
    $path = __SITE_PATH.'/classes';
    foreach( $pieces as $i ){
        $path .=  '/'.$i;
    }
    //echo "trying to include " .$path.".class.php";
    require_once( $path . '.class.php' );
}

Answer 1

I found the problem, apparently this function is not being called automatically. Here is the fix;

spl_autoload_register('__autoload');

This worked.