Question

I am new to PHP and am trying to build a facebook application. In the index.php file, I do the following :

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

the facebook sdk seems to start the session by itself, so my code, doesn’t get called at all ! meanwhile, index.php has a form that gets submitted to a new file called processForms.php. In index.php, i set the following:

$_SESSION['uid'] = $me['id'];

But in processForms.php, accessing $_SESSION gives me the following error:

Notice: Undefined variable: _SESSION

Not sure whether I am getting the whole concept of sessions wrong here.

Answer 1

You don’t need an if before session_start. Just call it straight: session_start();. If the session has already been started, it will do no harm.

It seems you get the concept of “starting the session” wrong. Well, not exactly wrong… Look: “session_start()” does not “starts the session”, in the sense you may be thinking, i.e., you call it once and the “session has been ‘started'”. No. You need to call “session_start” always, in the beginning of every PHP script which will deal with sessions.

For example, at login.php:

session_start();
if ($user_and_pass_are_correct)
{
    $_SESSION['username'] = $username;
}

At somepage.php:

session_start();
echo 'User name is ' . $_SESSION['username'];

You need the “session_start” call there. It does not mean “the beginning of the session”. It means “initialize the session stuff, so I can use sessions”.

An usual approach is to have a single session_start in a “bootstrap” kind of script, and include it in the beginning of all other scripts.

“bootstrap.php“

<?php
    session_start(); // first line of script
    initialize_other_stuff();

“a_page.php“

<?php
    include('bootstrap.php'); // first line of script

“another_page.php“

<?php
    include('bootstrap.php'); // first line of script, always