(PHP 5 >= 5.1.2)
spl_autoload_register — Register given function as __autoload() implementation
$autoload_function
   [, bool $throw = true
   [, bool $prepend = false
  ]]] )Register a function with the spl provided __autoload queue. If the queue is not yet activated it will be activated.
If your code has an existing __autoload() function then this function must be explicitly registered on the __autoload queue. This is because spl_autoload_register() will effectively replace the engine cache for the __autoload() function by either spl_autoload() or spl_autoload_call().
If there must be multiple autoload functions, spl_autoload_register() allows for this. It effectively creates a queue of autoload functions, and runs through each of them in the order they are defined. By contrast, __autoload() may only be defined once.
autoload_functionThe autoload function being registered. If no parameter is provided, then the default implementation of spl_autoload() will be registered.
throw
       This parameter specifies whether
       spl_autoload_register() should throw 
       exceptions when the autoload_function
       cannot be registered.
      
prependIf true, spl_autoload_register() will prepend the autoloader on the autoload queue instead of appending it.
   Returns TRUE on success or FALSE on failure.
  
| Version | Description | 
|---|---|
| 5.3.0 | Namespaces support was introduced. | 
| 5.3.0 | The prependparameter was added. | 
Example #1 spl_autoload_register() as a replacement for an __autoload() function
<?php
// function __autoload($class) {
//     include 'classes/' . $class . '.class.php';
// }
function my_autoloader($class) {
    include 'classes/' . $class . '.class.php';
}
spl_autoload_register('my_autoloader');
// Or, using an anonymous function as of PHP 5.3.0
spl_autoload_register(function ($class) {
    include 'classes/' . $class . '.class.php';
});
?>
Example #2 spl_autoload_register() example where the class is not loaded
<?php
namespace Foobar;
class Foo {
    static public function test($name) {
        print '[['. $name .']]';
    }
}
spl_autoload_register(__NAMESPACE__ .'\Foo::test'); // As of PHP 5.3.0
new InexistentClass;
?>
The above example will output something similar to:
[[Foobar\InexistentClass]] Fatal error: Class 'Foobar\InexistentClass' not found in ...