Introduction to PHP SESSION Variable

Introduction

As we know that http protocol is a stateless protocol so the web server does not recognize you . A PHP session solves this problem by allowing you to store user information on the server for later use (i.e. username, shopping items, etc). However, session information is temporary and will be deleted after the user has left the website. If you need a permanent storage you may want to store the data in a database.

Sessions work by creating a unique id (UID) for each visitor and store variables based on this UID. The UID is either stored in a cookie or is propagated in the URL.

What is session control?

Gives ability to track a user through site, and easily move data related to that user among pages.No need to move data through hidden form fields.
Very useful for authentication, but can be used any time persistent data needed throughout a site visit.

How sessions work

Sessions are identified by a random number (Session ID) generated by PHP and stored on the client computer in 1 of 2 ways:

1. Using a cookie, if the user's browser supports.
2. Appending the session number to URLs as user traverses site (i.e  www.whatever.com?PHPSESSID=495294532459x)

Session ID corresponds a session data store onserver
A session will eventually expire‐‐usually after aspecified period of inactivity.

Progression of events

PHP script starts a session. Done before any other page activity.

session_start();// Session ID created and stored on user's computer. (if possible)

Session variables are created, and values stored on the server.
PHP script can use these variables from page to page throughout a site.

Starting a session In PHP

In any script using sessions, you must first call

session_start();

•  If session has not been established, this will do that.
• If a session has been established, this will load session data.

You must start the session at the very beginning of the script‐‐as part of header transmission.
Add or access session variables by using the $_SESSION superglobal array.

Session Handling

Createa page ses1.php copy the following code in that page. and run it. now session will be set.

<?php
session_start();
$_SESSION['name'] = "your name";
$_SESSION['office'] = "company name";
$_SESSION['phone'] = 96951;
?>

Let's create another page ses_result.php copy following codes and run.

<?php
session start();

session_echo "Here's the session info:<br />";
foreach ($_SESSION as $var=>$contents)
echo "$var: $contents<br />";
?>

Manipulating the Session data

session_unset() erases all session variables and data.

unset() can be used to erase a single variable and data.

unset($_SESSION['myvar']);

session destroy() destroys the session data (without destroying the session variables).Can be useful for "logging out" user.

Session variable arrays

 Session variables can be arrays

<?php
session_start();
$_SESSION['list'][]="Hello";
$_SESSION['list'][]="Wow";
echo count($_SESSION['list'])."<br />";
foreach ($_SESSION['list'] as $item)
echo "$item<br />";
?>

Can be useful technique for shopping carts or other data that is accumulated over multiple page visits.

 

When and why to use Sessions

• Performance: When performing a slow operation, storing the results for use on several pages is better than repeating the calculation on each.
  Example: storing results of SQL query
• Sequence: When a user process takes place over a sequence of screens, storing information saves time and user input.

Personalization: Session variables can be used to store user color or layout preferences or facts about browsing activity. Pages can then adapt to that activity.