Get current contact id?

Question

I display the summary page for a civicrm contact and I need to get the current contact id. Is there any built in function for that?

I have this code where I explicitly refer to the civicrm id 4. Instead of doing that I would like to refer to the current civicrm contact.

$contact_id = 4;
$custom_name = array("custom_2","custom_3","custom_6","custom_7");
$params = array(
        'return' => $custom_name,
        'version' => 3,
        'id' => $contact_id,
);

$result = civicrm_api( 'contact','get',$params );

Answer 1

If you are on the contact summary screen, then the contact id is always $_GET['cid']. To give yourself peace-of-mind about using raw input, cast it to an integer.

$contactId = (int) $_GET['cid'];

Answer 2

The answer davejenx is correct but no longer considered best practice. Instead use:

CRM_Core_Session::singleton()->getLoggedInContactID();

Answer 3

Edit: The techniques below get the logged-in user's contact id. However the questioner has clarified that this isn't what they meant by "the current contact id". I'll leave this answer in place in case it's useful to someone else who misunderstood the question. Here's a simple way:

CRM_Core_Session::singleton()->getLoggedInContactID();

The above (for which thanks to Jon G) replaces this older technique:

$session = CRM_Core_Session::singleton();
$contact_id = $session->get('userID');

You can also do it by getting the user id from the CMS (Drupal / Wordpress / Joomla), then using the CiviCRM API to get that user's UFMatch record, which gives you the contact id.