php 得到session id

There are 2 ways to use sessions and session id's in PHP:

1 - Auto generate the session ID and get it:

session_start(); $id = session_id();

2 - Set the session ID manually and then start it:

session_id( 'mySessionId' ); session_start();

If you intend to set the session ID, you must set it before calling session_start(); If you intend to generate a random session_id (or continue one already started in a previous page request) and thenget that id for use elsewhere, you must call session_start() before attempting to use session_id() to retrieve the session ID.