class_exists Checks if the class has been defined boolclass_exists stringclass_name boolautoload This function returns &true; if the class given by class_name has been defined, &false; otherwise. ]]> class_exists will attempt to call &link.autoload; by default, if you don't want class_exists to call &link.autoload;, you can set the parameter autoload to &false;. ]]> The autoload parameter was added in PHP 5 See also interface_exists, and get_declared_classes.