How to tell what class you extends?

Is there a function that tells what class you are extending? Like function_exists?

I want to use this in开发者_JAVA百科 an __autoload function that if it detects a class that extends mysqli, then I will automatically connect it to the database.

class foo { };
class bar extends foo {};
$bar = new bar();
echo get_parent_class($bar);

assuming bar extends foo, should echo foo