JDT

John Dixon
Technology
Limited

Working with Session Variables in PHP

I can remember when I was learning to program in PHP a few years ago, people talking about things called session variables and thinking that it all sounded a bit scary. What were these things that people kept saying were so useful, and what were they used for?

Whenever I looked anything up on the Internet to do with session variables, the opening statement was normally something about HTTP being a stateless protocol - so I was lost straight away. What was a stateless protocol when it was at home?

In this tutorial I'm not going to use fancy technical terms to describe what session variables are and what they are used for, instead, I'm going to use plain English...or at least try to!

Let's start at the beginning. If I launch my web browser and open the home page of a web site, and then, from that page, click on a link to open another page on the same web site, the web server that sent the first page to my computer does not care that it is me who has also asked for the second page. The web server simply 'serves' pages as they are requested by a web browser - it doesn't keep track of who is requesting them.

In many cases this isn't a problem, because it doesn't matter that the web server doesn't know that it was me (or rather the web browser running on my computer) who requested both pages. However, if the web site requires me to log on in order to open subsequent pages on the site, the web server does need to know that it is me who is requesting the second page.

Session variables enable a web server to keep track of a web site visitor as they navigate around the site. Otherwise, you would have to log on to each page on the site individually, which would be a bit of a drag to say the least.

Session variables are simply variables that last for the duration of a session. This enables the web server to assign my login name, for example, to a session variable called, say, 'username', and then to check the value inside that variable for all pages that require me to be logged on in order to access them.

What is a Session?

What is a session? I can here you saying. A session is simply the time from when you start your web browser to when you close it. If you log on to a particular web site, and then navigate away from it to another site, you will (normally) still be logged onto the first site until you close the web browser. OK, there are other ways that might cause you to be logged off the first site, but in general, that's the way it works.

If, when you are developing a web site or application, you set up variable 'username' to contain the value 'john', when control moves to a different web page the value contained in the variable will be lost, unless you pass the variable and its contents from the first page to the second.

What this means is that if page 1 on the web site lets a user log on, when the user navigates to page 2 on the site (which, let's say, requires the user to be logged on in order to view that page), the fact that the user has already logged on will not matter, because the value will be cleared from the variable.

The use of session variables provides a good way of maintaining the values contained in variables from one web page to another, thus solving the problem described above.

Starting a Session

In order to use session variables on a web page, you need to start a session. You do this on every page where session variables are being used. The fact that you're starting a session that has already been started doesn't matter.

To start a session, type:

session_start();

Registering a Session Variable

Having started a session you can register session variables. So, to register a 'username' session variable and assign a value to it, we might have something like:

$_SESSION['username'] = "john";

Obviously, in a real situation, the value 'john' would not be hard coded like this, but would instead be obtained from a log on form of some sort.

Using a Session Variable

Now that we have registered 'username' and assigned a value to it, we can use it.

So, to check (on subsequent pages of the web site) that someone has successfully logged on ('john' in our case), we can use the following lines:

session_start();

if (isset($_SESSION['username']))

{

print "You have successfully logged on";

}

else

{

print "You have not logged on";

}

Finishing Off

When you have finished with a session variable, you can unset it. To unset 'username', use the following line:

unset($_SESSION['username']);

Finally, you should destroy the session:

session_destroy();

Author: John Dixon
John Dixon Technology Ltd

Go back to PHP Tutorials home page

Go back to Tutorials home page

Earnings Tracker is John Dixon Technology's FREE open source accounting / bookkeeping software tool.

Aimed at UK contractors and freelancers, Earnings Tracker enables you to perform bookkeeping and accounting tasks, helping you to keep track of your company's earnings and outgoings.

The software is written in PHP and MySQL and is available to use for FREE online, or as a FREE download.

Earnings Tracker can also be used simply as a dividend, corporation tax, or VAT calculator.

JDT

Privacy Statement

Terms & Conditions