php读取xml节点值,该如何处理

php读取xml节点值
获取的XML如下：

{"status":"failed","result":"未知错误"}

header('Content-type: text/html;charset=utf-8');
$s =
{"status":"failed","result":"未知错误"}
XML;

$x = @simplexml_load_string($s);
echo $x[0];