PHP条件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();
}

Answer 1

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.