PHP Sessions

What is PHP Session?

$_SESSION is a special array used to store information across the page requests a user makes during his visit to your website or web application.

Although you can store data using cookies but it has some security issues. Since cookies are stored on user’s computer it is possible for an attacker to easily modify a cookie content to insert potentially harmful data in your application that might break your application.

Also every time the browser requests a URL to the server, all the cookie data for a website is automatically sent to the server within the request. It means if you have stored 5 cookies on user’s system, each having 4KB in size, the browser needs to upload 20KB of data each time the user views a page, which can affect your site’s performance.

You can solve both of these issues by using the 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 or SID. This unique session ID is used to link each user with their own information on the server like emails, posts, etc.

How to Start PHP Session

Before you can store any information in session variables, 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 session ID for the user.

The PHP code in the example below simply starts a new session.

<?php
// Starting session
session_start();
?>

The session_start() function first checks to see if a session already exists by looking for the presence of a session ID. If it finds one, i.e. if the session is already started, it sets up the session variables and if doesn't, it starts a new session by creating a new session ID. 

<?php
// Starting session
session_start();
// Storing session data
$_SESSION["firstname"] = "Peter";
$_SESSION["lastname"] = "Parker";
?>

<?php
// Starting session
session_start();
// Accessing session data
echo 'Hi, ' . $_SESSION["firstname"] . ' ' . $_SESSION["lastname"];
?>