PHP's date functions are powerful, flexible, and surprisingly easy to use. This section guides you through the functions, explaining the concept of a Unix timestamp, which is at the heart of most of the functions.

Server Side Includes

You can insert the content of one file into another file before the server executes it. include and require functions are used include others functions, headers, footers, or elements that will be reused on multiple pages.

This can save the developer a considerable amount of time. If all of the pages on your site have a similar header, you can include a single file containing the header into your pages. When the header needs updating, you only update the one page, which is included in all of the pages that use the header.

Example

The following example includes a header and footer that should be used on all pages:

Date & Time

PHP's date functions are powerful, flexible, and surprisingly easy to use. This section guides you through the functions, explaining the concept of a Unix timestamp, which is at the heart of most of the functions, and shows you how easy it is to master these often-misused functions.

Displaying the current date and time with the date function

date is the most used function that returns the current date and time and allows you to format as you wish.

There are a whole range of possible formatting options. You can add your own characters inside the format string too. Here's a list of all the formatting characters:

Since PHP 5.1.0 (when the date/time functions were rewritten), every call to a date/time function will generate a E_NOTICE if the timezone isn't valid, and/or a E_STRICT message if using the system settings or the TZ environment variable.

Examples

The '-' character are my formatting strings. I could have used anything else too:

Read through the list above, you'll find most possibilities have been thought of, and if all you're trying to do is format the date and/or time, you'll have no problems.

date function is not only tied to displaying the local date/time on the server. You can also pass it a timestamp (often called a Unix timestamp), which is the number of seconds since January 1, 1970 (starting with 1 second after midnight). By default the date function takes the current timestamp, but you can pass any timestamp you want, for example:

Be careful though with trying to use one of the reserved format strings as your own format string. If you tried to do something like:

you'd get something like the unexpected result of UTC06UTC 310503UTC 0501 06:05.

Of the first word, The, the 'T' returns the timezone setting of the machine running PHP (UTC in my case), 'h' returns the hour, and 'e' returns the timezone identifier. But from there it's all downhill. In order to get the correct display, you'll need to escape the characters with a backslash, as follows:

which displays what we'd originally hoped for The time is 06:05.

Just for good measure we had to escape the 't' twice, since \t is the special character for a tab. Not the easiest to read at all!

There is also a related gmdate function, which is identical to the date function except that the time returned is Greenwich Mean Time (GMT).

Cookies

Cookies in PHP are not difficult to implement, and there are only two commands that need to be used with them. PHP makes it easy to set and read cookies and provides all the features needed to give their details.

Setting a basic cookie

The PHP function for setting cookies is called setcookie.

The most basic information for a cookie is his name and his value. The name of the cookie must be something which you can refer to it later as. You don't need to worry about it clashing with other sites as cookie names are domain specific, but you should try and use a descriptive and unique name for your cookies.

For this first example, assume that you have used PHP to load the user's name into the variable $name and want to greet the user in the future by their name. You would need to create a cookie which stores their name as follows:

This creates the most basic of cookies, storing the user's name in a cookie called nameOfUser. By setting cookies like this, you don't set any specific options, so by default the cookie will be available to the domain in which it was set (e.g. example.com) and will be deleted when the user closes their browser.

Reading cookie values

PHP makes it extremely simple to read the value of a cookie. In PHP, reading form values are achieved using $_GET and $_POST. PHP has a similar global variable for cookies:

This variable contains the value of the cookie with name CookieName. So on your website, if you want to display the name of the user, you could simply use the following:

Of course, the user may not already have the cookie, so you should use the PHP function isset. This returns true if a variable has been set and false if not. Using this, your site could do the following:

Cookie settings

Although the code I have given you allows you to set a simple cookie on the user's computer, it isn't very powerful. Mainly because it's lost when the browser is closed. One of the most powerful features of cookies is the ability to set an expire date. The cookie will remain on the user's computer until it expires, then it will automatically delete itself.

This code takes the current time (time function), then adds 3600 seconds to it, and uses this value to set as the expire time for the cookie. Basically this means that the cookie will remain on the user's computer for an hour (it expires 3600 seconds from the current time).

There are three other options which can be used when setting cookies:

The path

This refers to where in the domain you are able to access the cookie in future. By default this is the current directory (so if you set the cookie in the page http://www.example.com/subfolder/setcookie.php, it would only be available to scripts in the subfolder directory and below). You can set this to any part of your site, which can be useful in some situations.

The domain

By default, a cookie is only available in the domain you set it in, for example if you set the cookie on example.com you can only ever access it from example.com (even subdomains like mail.example.com can't access it). The most common need to change this setting is to allow the cookie to be viewed across all subdomains on a site. This can be done by setting the domain to .example.com (with both '.'s). By doing this anything .example.com is accepted (like mail.example.com).

Security

If this is turned on, the cookie will only ever be surrendered to the site over a secure connection - HTTPS.

The cookie set here, is called nameOfUser and again stores the value $name.
It will expire an hour from the current time.
It's available in all directories of the site (/ is the root directory).
It's available across any subdomain of the site example.com as .example.com has been given as the domain.
The final 1 means that this is a secure cookie and can only be transmitted over a secure connection. This would be 0 for a standard (non-secure) cookie.

Deleting cookies

There are occasions on which you may wish to delete a cookie from a user's computer. This could be if, for example, you want to log the user out of a system. Deleting a cookie is quite simple to do, all you have to do is to set the expiry time in the past. By doing this, the cookie will be automatically deleted as soon as it is created, and will remove any data that already exists there.

Sessions

Whenever you want to create a website that allows you to store and display information about a user, determine which user groups a person belongs to, use permissions on your website or you just want to do something cool, sessions are vital to each of these features.

You may be thinking right now, well that's nice, but I can do this with cookies! This may come to you as a surprise, but cookies are about 30% unreliable right now and it's getting worse every day. More and more web browsers are starting to come with security and privacy settings and people browsing the net these days are starting to frown upon cookies because they store information on their local computer that they do not want stored there. PHP has a great set of functions that can achieve the same results of cookies and more without storing information on the user's computer. Sessions store the information on the web server in a location that you chose in special files. These files are connected to the user's web browser via the server and a special id called Session ID. This is nearly 99% flawless in operation and it is virtually invisible to the user.

Avoiding errors

The first thing about sessions is that you MUST call the session_start function before anything is output to the web browser. This is absolutely important because you will get some ugly errors.

As you can see, that is one unattractive error to be displayed on your website. Why did it happen? It happened because I called echo before I called the session_start function. If I had swapped the lines around I would not have this error.

Starting your session and assigning variables

Let's say that we had an input form from a page that asks the user their name. This form will post to a PHP script that will get the post information and register it as a session variable that we can use throughout our website until the user leaves the site or until we unregister that variable.

As you can see there is absolutely nothing cosmic about that form. It is only an HTML page form.html that will post to a script register.php:

The important elements in the above codeblock are $_SESSION["name"] and that's about it. The rest is just standard HTML and PHP. If everything worked properly and you typed Bob in the form on the first page, you'll get the following output:

We've accomplished the following tasks:

• starting a session;
• posting a form to a PHP script;
• registering a session variable with a value;
• and displaying that session value in the browser.

Keeping the session across multiple pages

One reason why we register sessions is to avoid reading cookies and querying databases for information about the user on each page we need that information on.

The first thing you MUST do on each page you want to access a session variable is to start the session. That may not sound right to you because you may be thinking We already started the session on the last page, that's true, but we need to keep the connection going between our session because they do not have persistent connections like a database does.

Here's the next script called testSession.php. You may have noticed it in the code examples above.

The first few chunks are pretty self explanatory by now if you have been following this tutorial closely. We started the session, called the session variable and echoed:

Hey Bob. Everything is still working!

Pick an option:

• Delete the session variable now!
• Destroy the session!

Now you can see how the session variables can be used on multiple pages.

There is also a couple of hyperlinks to two more scripts, delete.php and destroy.php.

Unregistering session variables

With sessions we have the ability to simply remove a single session variable without dumping our entire session and rebuilding it. We can simply do this by assigning a blank value or false to the session key we want to get rid of.

Destroying a session

Anytime you have a login feature you should have a logout feature as well. That's where the function session_destroy comes in handy. session_destroy will completely clear any trace of the session.

If you are using the $_SESSION superglobal array like we are in this tutorial, you must clear the array values first, then run session_destroy.

Now that we've covered the basics of session handling such as start a session, register a variable, assign a value to the variable, unregister the session variable and destroy the session, let's go ahead and use this knowledge implementing a session hit counter to display how many pages the user has clicked on during their visit to our site.

Session examples

Page Hit Counter

What we're about to do is start your session, register a variable called count and assign a value of 1 to it on the first page increment.php. Then, we're going to increment the counter as we go through the website.

If the session variable count has no value or is equal to 0, set it to a value of 1, otherwise increment it each time this code is called.

$_SESSION['count']++; is simply saying add 1 to the current value of count.

Next, we've given the user a page reset.php to reset their counter. This is nearly the same code as above, except we aren't doing the error checking because we just want to reset the counter to 1 when the user access that page.

Listing your session variables and values

This script is very useful to view which information is actually being stored in your user's sessions.

The script is pretty straight forward and will give you all the information you need to know about what is in your session's scope. If you have a $_SESSION["name"] variable with the value John, a possible output can be:

Sessions list:

Array
(
[name] => John
)

Viewing your Session ID

The function session_id allows you to display the current Session ID or use it however you need.

Your Session ID is 167jDFYp3sTAAAASey0qL6

File handling in PHP

Manipulating files is a basic necessity for serious programmers and PHP gives you a great deal of tools for creating, uploading, and editing files.

File open

fopen function is used to open files in PHP.

The first parameter of this function contains the name of the file to be opened and the second parameter specifies in which mode the file should be opened in.

List of possible modes for fopen:

If the fopen function is unable to open the specified file, it returns 0 (false).

File close

fclose function is used to close a file.

End of file

feof function is used to determine if the end of file is true.

You cannot read from files opened in w, a, and x mode!

Read a character

fgetc function is used to read a single character from a file.

The file pointer move to the next character each time this function is called.

File delete

When you view the contents of a directory you can see all the files that exist in that directory because the system displays a list of filenames. You can think of these filenames as links that the system has created to link a directory with those listed files.

If you unlink a file, you are effectively causing the system to forget about it or delete it!

Before you can delete a file, you must make sure that the file isn't open in your application. Use fclose function to close down a file.

To delete the file file.txt simply run a PHP script that is located in the same directory. unlink function just needs to know the name of the file to start working its destructive magic.

File upload

A very useful aspect of PHP