Both functions are defined in qa-app-cookies.php.
function qa_cookie_get() → "Return the user identification cookie sent by the browser for this page request, or null if none"
function qa_cookie_get_create() → "Return user identification cookie sent by browser if valid, or create a new one if not. Either way, extend for another year (this is used when an anonymous post is created)"
This question originated from finding a bug in the badges plugin where qa_cookie_get_create() is called:
'INSERT INTO ^eventlog (datetime, ipaddress, userid, handle, cookieid, event, params) '.
'VALUES (NOW(), $, $, $, #, $, $)',
qa_remote_ip_address(), $user_id, $handle, qa_cookie_get_create(), 'badge_awarded', 'badge_slug='.$badge_slug.($object_id?"\t".'postid='.$object_id:'')
I replaced qa_cookie_get_create() with qa_cookie_get() and would like to know about side effects.