PHP and Cookies; a good mix! by Dennis Pallett
Introduction Cookies have long been used in PHP scripts, and are a very
useful function. But what exactly are cookies? Maybe you have used then, but
you still don't know exactly what they are. Or you are completely new to
cookies? It doesn't matter, because in this tutorial I will show you exactly
what cookies are, and what they are used for.
Cookies in a nutshell Cookies are small pieces of information that is
stored on the computer of your visitors. Each browser handles it differently,
but most simply store the information in a small text file. Internet Explorer
has a special folder, which can be found in your C:Windows or C:WindowsSystem32
folder. You can delete all your cookies, by going to the Options and 'Clearing
Cookies' or deleting them by hand. I don't recommend this though.
Almost every website uses cookies. If you go to Amazon.com, you will get
several cookies. The same goes for CNN.com. Even Google uses cookies! They are
extremely useful for (temporarily) storing information. For example, if you
have a login system for your visitors, you could save their userid and password
(very heavily encrypted!) so they are automatically logged in the next time
they visit your website.
Or you could remember their last visit, and highlight everything that is new.
And that's just the beginning.
Using Cookies Using cookies in PHP is extremely easy. In fact, there is
nothing to it, because of PHP's inbuilt setcookie()
function. Have a look at the documentation, and then try the following
example:
<?php
// Set a cookie // Cookie name: name // Cookie value: Dennis Pallett // Cookie
expire: in 24 hours
setcookie ('name', 'Dennis Pallett', time() + (60*60*24)); ?>
If you run the code above, then a cookie will be set. That's all. The cookie
name and value are pretty obvious. The cookie expire is when the cookie
expires, or goes away. Simply use the time() function
and add the number of seconds you want to have the cookie available to it. In
the example I added 60*60*24=86400 seconds, or 24 hours.
If you have looked at the documentation, you probably noticed there are
additional arguments. As the documentation says, the path is to limit a cookie
to a specific path on your web server. This is often used when you run multiple
instances of the same script in separate directories. You can safely omit this
argument when it doesn't matter if the cookie is available site-wide.
There is also the domain argument. This can be used to limit the cookie to a
specific sub-domain, e.g. test.example.com. You can also safely ignore this
argument, or set it to .example.com (note the beginning period, this is
essential!).
Finally, there is also the secure argument. This argument is only used for
cookies that are sent over a secure HTTPS connection (SSL). Just ignore this
argument, unless you're working with a secure connection.
One thing that should be mentioned is that cookies must be set, before you
display any HTML/text. It's probably best if you turn on output buffering by
putting ob_start() at the top of your
page.
Now that you have set a cookie, you probably want to retrieve the value as
well. After all, that is the whole point of using cookies. Thankfully, as PHP
is ever so easy, you can retrieve the same way as you retrieve a GET value. See
the following example to retrieve the value of the previous example:
<?php echo 'Your name is ' . $_COOKIE['name']; ?>
This should print "Your name is Dennis Pallett". There's nothing more to it.
It's just that easy!
Finally, one thing you probably want to do as well is remove cookies. This is
as easy as setting them. Simply change the value of the cookie to FALSE, and
change the expire date to -3000 seconds. See the following example:
<?php setcookie ('name', FALSE, time()-1000); ?>
Checking if cookies are enabled Before you start using cookies, you must
make sure your visitor has cookies enabled. This can be done with a simply PHP
checking script. Unfortunately, the PHP page needs to reload to check for
cookies. But this can be done very transparently, and your visitor should
hardly notice anything.
The following example will first set a test cookie, then reload the page, and
finally check whether cookies are enabled.
<?php error_reporting (E_ALL ^ E_WARNING ^ E_NOTICE);
// Check if cookie has been set or not if ($_GET['set'] != 'yes') { // Set
cookie setcookie ('test', 'test', time() + 60);
// Reload page header ("Location: checkcookies.php?set=yes"); } else { // Check
if cookie exists if (!empty($_COOKIE['test'])) { echo "Cookies are enabled on
your browser"; } else { echo "Cookies are <b>NOT</b> enabled on
your browser"; } } ?>
Run the code above, and see what the output is. Check if cookies are enabled in
your browser. If they're not enabled, then you can enable them by going to your
browser's options. Unfortunately, this is different from each browser, so I
can't give you exact instructions. But Google can.
Storing Arrays One feature of cookies that is often missed in articles
is the ability to story arrays. Cookies can be used to store multi-dimensional
arrays, which can be extremely useful to store data.
Consider the following code;
<?php setcookie ("name[first]", "Dennis", time() + (60*60*24)); setcookie
("name[last]", "Pallett", time() + (60*60*24)); ?>
You can then display these two cookies using the following code:
<?php echo "First Name: " . $_COOKIE['name']['first']; echo "<br
/>Last Name: " . $_COOKIE['name']['last']; ?>
The cookie 'name' is an array, and has multiple values. You can even go deeper
and have multi-dimensional arrays, e.g.
$_COOKIE['name']['test']['something']['value']. You could store whole arrays of
data in cookies. But beware that you don't store too much data, there are
certain size limits to cookies.
In Conclusion... Cookies are really versatile, and can be used for a lot
of different purposes. Many websites use cookies, and cookies can really make
your website more personalized. Using cookies in PHP isn't hard at all, and you
should be able to use them without any difficulty.
Before actively using cookies in your website, you must check whether the
visitor has enabled them in their browser. If they don't have cookies enabled,
you must either redirect to a non-cookies version of your website, or you can
make sure your website also works without cookies.
You can download a sample script at
http://www.phpit.net/demo/php%20and%20cookies/logger.zip,
where cookies are used in a (somewhat) practical way. In this example, there is
a logging module, called log.php and a display module, called history.php.
Basically, you include the log.php in other PHP pages, and then you can view
history.php to lookup all the pages you have viewed and how often. The example
uses arrays, and stores them in cookies.
The examples in this article can be downloaded at
http://www.phpit.net/demo/php%20and%20cookies/examples.zip.
If you have a really unique practical way of using cookies, please let me know
at dennis [AT] nocertainty [DOT] com. I'd really like to hear about interesting
ways of using cookies.
About the Author
Dennis Pallett is a young tech writer, with much experience in ASP, PHP and
other web technologies. He enjoys writing, and has written several articles and
tutorials. To find more of his work, look at his websites at
http://www.phpit.net,
http://www.aspit.net and
http://www.ezfaqs.com
|
