If you're using PHP (and perhaps MySQL with it) to make as much of your site dynamic as possible, you won't be able to make a site truly interactive and tailored to individual users unless you use something more. Something like "cookies."

Using Cookies in PHP

It's got to happen sooner or later. Even if you're using PHP (and perhaps MySQL with it) to make as much of your site dynamic as possible, you won't be able to make a site truly interactive and tailored to individual users unless you use something more. Something like "cookies."

Cookies, unfortunately, have been given a bad rap. I once, during an Internet Safety Course, was told (from a police officer, no less!) that if I visit a site, the owner of the site could use something called a "cookie" to view my name and address. I refrained from correcting the officer, but was tempted to. The statement was very far off.

Cookies are tiny files containing text stored on your computer. A website can set them, and read from them. They can read different things about your visit, such as your IP address, or perhaps your screen resolution. Or, the pages you visited and forms you filled out. They cannot, however, read your name and address if you don't provide them with it.

Now that that's out of the way, let's get started. Let's create a page that sets a simple cookie (name it "setcookie.php", or "setcookie.php3", depending on your server's settings):

This is fairly simple. We're using PHP's built in "setcookie" function. As you can see, it accepts several arguments. The first argument, within double-quotes, is the name of the cookie. In this case, it is "user" - we're storing a username. The second argument is a variable, obviously given a value beforehand. The third argument specifies the length that the cookie should be considered "active" - or, in other words, determines the expiration date at which the cookie is discarded.

In this case, we have it set to expire in one week. The number you see there (604800) is the number of seconds in a week, and the text after the setcookie command is a small comment informing us of how long it will take for the cookie to expire. Using comments, in this case, is a very good idea. This way, we don't have to memorize how many seconds make up a day, a week, or a month.

Here's a small reference on numbers and the amount of time they signify in determining the expiration date/time of a cookie:

You can probably work with these numbers to determine how many seconds are in any given amount of time. Be sure to have a calculator handy, though! If you lack a real-life calculator, Windows users can click on their Start Menu, choose "Run", and type in "CALC."[PAGEBREAK]Using the earlier command, you'll create a cookie, accessible only on your domain name, with the name "user." This cookie's value, if called upon, will be whatever the variable $username holds. You could have just as easily replaced $username with any string of text to specify the value of the cookie, provided that the string is enclosed in double-quotes and escapes any inappropriate characters within.

So, how do we read from a cookie? Well, at times, you can simply reference the name of the cookie as a variable - in this case, $user. However, I consider it good practice to specifically grab the value of the cookie and assign it an appropriate variable - this is useful if you wish to use one name for the actual cookie, but access it's value from a variable of a different name. For example:

Simple, isn't it? We're using a simple assignment operation to grab the value of the "user" cookie and give it a name we can use within our script: $user. You can easily replace $user with $username, $userid, or $purplebanana - whatever you want.

Now, there will likely come a time where you will want to allow your users to logout of whatever system you choose to build with your newfound cookie knowledge. This is almost just as easy as setting a cookie:

This is pretty simple: we have to specify the name of the cookie, as expected. We do not need to specify any value for the second argument, as is indicated by the two double-quotes without anything in-between. After this, we have the usual number of seconds used to set the cookie's expiration date, with one crucial difference: can you guess what?

If you noticed the "minus" sign, negating the number after it, then congratulations, you get a cookie. Any cookie set for an expiration date that is in the past is discarded. So, technically, we're using the "setcookie" function, but not to set a cookie. Maybe a tad confusing, but not a big deal.

As for the number of seconds: we could, if we wanted to, set it to "-1", and it would probably work just as well. However, due to possible variances between computer times, dates, and even time zones, you might as well set it the number of seconds in a week. That way, you avoid any possible risks, and the extra work is almost non-existent.

A word of warning before I depart: you should always set, delete, and declare cookie variables before producing any output on your page - even whitespace. For example, the below code would produce an error (I've specified the value of the cookie with a string of text rather than a variable this time, to combine two examples into one):

However, this next block of code would work just fine:

This applies to almost all references to cookies - so make sure nothing has been printed to a webpage in any way whatsoever before reading from, setting, tossing (just kidding), and deleting your cookies. This includes echo commands, print commands, printf commands, sprintf commands, or HTML.

Congratulations if you've made it this far (you didn't skip right to the end, did you? This isn't a whodunit...it'll do you no good!), you now know how to set cookies, read from them, and delete them.