Session In PHP. Everything You Need To Know

Not that you learn what are cookies, how to create them and how to delete them, it’s time to move even further and talk about sessions. In this article you will learn what sessions are, how to create and how to destroy a session in PHP.

What Is Session In PHP

If you red last post on this blog, you know that you can store data using cookies. But it has some security problems since cookies are stored on user’s computer. It is possible to easily modify a cookie content to insert potentially malicious data that might break your application.

Also cookies can affect your website’s performance because every time browser sends a request to the server, all the cookie data for a website is sent. It means that if you have stored 5 cookies 4KB in size on user’s computer, the browser needs to upload 20KB of data each time the user views a page.

But you can solve both of these issues by using PHP session. A PHP session stores data on the server rather than user’s computer. In a session based environment every user is identified through a unique number called session identifier (SID). This unique session ID is used to link each user with their own information on the server. For example emails, pots etc.

How To Start a PHP Session

In order to store any information in session, you must first start up the session. To begin a new session, simply call the PHP session_start() function. It will create a new session and generate a unique ID for the user.

Here is the example of how to start a new session:

<?php

session_start();
?>

The session_start() function checks if a session already exists by looking for the session ID. If the session is already started, it sets up the session variables and if it doesn’t, it starts a new session by creating a new session ID.

How To Store And Access Session Data

You can store all your session data as key – value pairs in the $_SESSION[] superglobal array. The stored data can be accessed during lifetime of a session. Here’s the script which creates a new session and registers two session variables.

<?php

session_start();
 

$_SESSION["firstname"] = "Web";
$_SESSION["lastname"] = "Stuff";
?>

And now here is the example of how to access data that you have stored in session:

<?php

echo 'Hi, ' . $_SESSION["firstname"] . ' ' . $_SESSION["lastname"];
?>

Your result would be:

Web Stuff

How To Destroy A Session

Let’s say you want to remove certain session data. In that case simply unset the corresponding key of the $_SESSION associative array:

<?php
if(isset($_SESSION["lastname"])){
    unset($_SESSION["lastname"]);
}
?>

And if you want to destroy a session completely, call the session_destroy() function. This function does not need any argument and a single call destroys all the session data.

<?php

session_destroy();
?>

Worth noticing that every PHP session has a timeout value or duration which is measured in seconds. You can adjust this timeout duration bu changing the value of session.gc_maxlife variable in the PHP configuration in php.ini file.