从simplexmlelement对象获取值

I'm having trouble with converting my simplexmlelement object to variables. This is my xml output:

<affiliate_signup_response>
  <success>false</success>
  <message>Duplicate Affiliate Contact</message>
  <affiliate_id>0</affiliate_id>
</affiliate_signup_response>

Now i've searched the net and found out that I have to do something like this to get the output:

(string) $xml[0]->succes;
(string) $xml->succes;
(string) $xml->affiliate_signup_response->succes;

I just can't seem to get the right response and am probaly missing the right clue into making this work. I really hope this is not a dumb question.

If create a foreach loop with $key and $value this is the output:

key: success value: false
key: message value: Duplicate Affiliate Contact
key: affiliate_id value: 0

Try

$str = <<<XML
<affiliate_signup_response>
  <success>false</success>
  <message>Duplicate Affiliate Contact</message>
  <affiliate_id>0</affiliate_id>
</affiliate_signup_response>
XML;


$xml = new SimpleXMLElement($str);
//var_dump($xml);
$success = $xml->success;
$message = $xml->message;
$affiliate_id = $xml->affiliate_id;

echo $success."<br />";
echo $message."<br />";
echo $affiliate_id."<br />";