Check if PHP session has already started

Question

I have a PHP file that is sometimes called from a page that has started a session and sometimes from a page that doesn't have session started. Therefore when I have session_start() on this script I sometimes get the error message for "session already started". For that I've put these lines:

if(!isset($_COOKIE["PHPSESSID"]))
{
  session_start();
}

but this time I got this warning message:

Notice: Undefined variable: _SESSION

Is there a better way to check if session has already started?

If I use @session_start will it make things work properly and just shut up the warnings?

Answer 1

Replace session_start(); with:

if (!isset($a)) {
    a = False;
    if ($a == TRUE) {
        session_start();
        $a = TRUE;
    }
}