session_status

Maybe depending on PHP settings, but if return values are not the above, then go for this:_DISABLED = 0_NONE = 1_ACTIVE = 2

Use always session_status(), to check if a session is already started and active.if(session_status() !== PHP_SESSION_ACTIVE) session_start();or if(session_status() === PHP_SESSION_NONE) session_start();Don't useif(!isset($_SESSION)) session_start();orif(session_id() === "") session_start();They will not work properly after a call to session_write_close().Both functions will continue to report, that the session exists.And this is right, you can read from $_SESSION, but if you want to write,you need session_start() again.As a shorthand you can use @session_start() with the @ at the beginning to suppress the PHP notice "A session had already been started - ignoring session_start()"As stated in the manual for session_start(), a second call will do no harm,it will be simply ignored. But you need the @, if you don't want to get the notice.

Universal function for checking session status.<?php/** * @return bool */function is_session_started(){    if ( php_sapi_name() !== 'cli' ) {        if ( version_compare(phpversion(), '5.4.0', '>=') ) {            return session_status() === PHP_SESSION_ACTIVE ? TRUE : FALSE;        } else {            return session_id() === '' ? FALSE : TRUE;        }    }    return FALSE;}// Exampleif ( is_session_started() === FALSE ) session_start();?>

Note session_status() is for file based session only.DB based session status needs to have custom function based on table structure.

The advice of ive_insomnia at live dot com should be taken with great care.First of all, while his use case for session_status is valid, a simpler way to avoid the warning is:<?phpif (!isset($_SESSION)) { session_start(); }?>The example of session_status uses the raw values of constants (2 in this case) created specifically for the purpose of not having to use magic numbers.Better code would be:<?phpif (session_status() !== PHP_SESSION_ACTIVE) {session_start();}?>The same can be done using<?if (session_id() === "") { session_start(); }?>The use of this function is lies more towards status management: change the behavior of a script when sessions are disabled altogether, for example.

This is how the session_status() works:<?phpfunction session_status(){    if(!extension_loaded('session')){        return 0;    }elseif(!file_exists(session_save_path().'/sess_'.session_id()){        return 1;    }else{        return 2;    }}?>

Just another function to determine whether the session has already started:function is_session_started () {    return function_exists ( 'session_status' ) ? ( PHP_SESSION_ACTIVE == session_status () ) : ( ! empty ( session_id () ) ); }

If you started and closed a session then test ( session_id() === '' ) to check if a session is active it won't work, session_id() returns an ID even if the session is closed.Anybody knows another way before PHP 5.4 to check if a session is really not currently active ?