how to reliably detect if session is started

[sfullman]

I want to find out reliably if session_start() has been called in at least one section of the script. How would I do this?

Thanks,
Sam

[Frederick]

if (isset($_SESSION['sess_name'])) {
    // session read and good
} else {
    // no session, do something else
}

[Weedpacket]

See if session_id() is nonempty?