PHP conditional session_start

Question

I have the following in my PHP header from an existing little web app. My question is: doesn't this make the page jump through an extra step to first check and then start a session? What is the point of this?

If a session exists, can't I just use session_start and if it does not won't it be ignored?

PHP

if (!isset($_SESSION)) {
   session_start();
}

So you don't do too much work by starting the session 10.000 times by accident. — Tdelang
– Tdelang, Commented Aug 8, 2013 at 13:58
Kind of strange, but it depends on where it is. If it's in a function, for instance, or a file that is likely to be included in multiple places, then like Tdelang said, it's so you don't start a session when it's already started. In fact it's more than just saving time: I think if you call session_start() when there's already an existing session, it will replace that session. If it's in a place where it is only going to be called once, then it seems superfluous, but doesn't do any harm. — brianmearns
– brianmearns, Commented Aug 8, 2013 at 14:01

Scott Helme · Accepted Answer · 2013-08-08 14:02:34Z

5

If you call session_start() and no session exists it will create a new session. If there is an existing session it will resume that.

answered Aug 8, 2013 at 14:02

Scott Helme

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Rudi Visser · Accepted Answer · 2013-08-08 14:19:15Z

3

If I'm not mistaken, the $_SESSION superglobal will always exist, so your code won't really do very much anyway.

If you're on PHP <5.4, use the following code instead:

if (session_id() == "") {
    session_start();
}

On PHP 5.4+, use this:

if(session_status() != PHP_SESSION_ACTIVE) {
    session_start();
}

You should only really be calling session_start() once, but as @ScottHelme said, calling it multiple times will not have a negative effect, the session will be either created or resumed every time.

answered Aug 8, 2013 at 14:19

Rudi Visser

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