php json解码curl_exec在Facebook上共享链接的结果

I use curl php to share link on facebook all is fine and I'VE got this result { "id": "the_link_id" }. I tried to got the id with:

$result = curl_exec($ch);
$json = json_decode($result);
$post_id = $json->{'id'};
echo $post_id;

but I got this error:

Trying to get property of non-object ...

i found the solution i just added curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);