Get the URL of the .swf-file

I want to check what the name of the file containing my .swf-file is.

I’ve tried something like:

createObjectFromURLEncoded();

function createObjectFromURLEncoded() {
var query:String = flash.external.ExternalInterface.call(“function get_url() { return window.location.toString(); }”).split("?")[0];
_root.testtxt.text = query;
}

where my dynamic text-field should display the name of the file (for example index.php). But it doesn’t work. Any ideas?