PHP Sessions

Session

Sessions use cookies. Cookie holds only reference to server, where the data is actually stored.
Advantages / differences over cookies:
- Session data is stored in a file on server.
- Large amounts of data can be saved to server
- Client-side cookie is very small, saves bandwith
- Session lasts until user closes browser
- More secure

Session is a combination of client-side cookie containing reference to server data.
The server data file and cookie is created using session_start() - function
If session already exists, session_start() loads the session data. Otherwise it creates a new cookie and server data file.
Each visitor has a unique session file.
session_start() must be called before printing any html. Also it must be called everytime when trying to access the server data

All session data is accessible via $_SESSION array. Adding values is done in same way than in any array.
=> now the values are accessible when user goes to another page

Adding session data:

$_SESSION['var'] = "foo";
$_SESSION['login'] = "true";

Reading the session data is easy. Just use the $_SESSION array to get the data you need.
Session data is available as soon as it is set

Example:

$_SESSION['var'] = "foo";
$_SESSION['login'] = "true";
print $_SESSION['login'];
print $_SESSION['var'];

To delete session data, use unset(..) function.
unset($_SESSION['var'])
Session lasts until the user closes their browser. If you want to delete the session before that, clear the whole $_SESSION array and use session_destroy() function

Example of deleting the session:

session_start();
$_SESSION = array();
session_destroy();