How to retrieve Mailchimp campaign id using api v3 - php

Question

I'm new to the Mailchimp api v3.0 (using php). I've created a campaign with the api and want to retrieve the campaign id from the cURL return data but can't seem to extract just the id. I've been away from php for awhile so I guess I'm just being brain dead. Clearly, I can print the entire result but just need to extract the campaign id in order to add/update content. Most of the test code follows. How do I extract just the id from $retval?
$json_data = json_encode($options);
$auth = base64_encode('prcAdmin:'. $apikey);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'https://usn.api.mailchimp.com /3.0/campaigns');
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content_Type: application/json',
'Authorization: Basic ' . $auth));
curl_setopt($ch, CURLOPT_USERAGENT, 'PHP-MCAPI/3.0');
curl_setopt($ch, CURLOPT_TIMEOUT, 30);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, $json_data);
$retval = curl_exec($ch);

Answer 1

A few typos in your code, let's fix them first.
An extra space in the url
Content_Type to Content-Type. Good to correct it, though the endpoint returns data in a JSON format.
Assuming that you have a valid Auth with valid campaign data, it should return campaign data in JSON format. To extract the campaign id is pretty easy.
$campaign = json_decode($retval, true);
$campaignId = $campaign['id'];
If you can't get correct a campaign id, try to print out the result by using print_r($retval);. The correct data should look similar to an example response found on this page - http://developer.mailchimp.com/documentation/mailchimp/reference/campaigns/. (From and between curly brackets).

Answer 2

I resolved the problem: I added a:
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
and it obviously returned the response differently so the "id" tag could be referenced as:
$id = json_decode($retval);
echo $id->id;
Now it extracts just the "id".