Part 5.1PHP includes

HTML becomes a burden when every page needs updated with something like a change in the menu.

PHP, being a server side language, can generate this code for you, but then the problem is still there if the code needs to be changed on every page.

Reusable PHP is a very handy way of saving on server space. By duplicating PHP, the amount of space being used doubles. This can be fully avoided, as with any programming language such as C or Java.

include

In PHP, reusing code is achieved using the include method.

include in PHP could be seen as a more advanced version of the file_get_contents function that performs a similar function. Both of these can read any type of file and turn it into something to use, but the difference is that if the file_get_contents function is used on a PHP file, it will read the PHP file as text whereas the include construct will include the PHP as executable PHP (and will execute it).

The following example demonstrates a page which uses another page found at 'php/login.php' which contains functions such as the isLoggedIn function:

<?php
	include "php/login.php";
	$isLoggedIn = isLoggedIn();

	if ($isLoggedIn)
	{
		echo "<h2>New articles</h2>";
		echo "<p>Our articles are shown below:</p>";
		//TODO: Need to include some access to the database
		echo "All articles are copyright";
	}
?>
		

The main advantage of using the include construct is that if the code needs to be updated, only that file is changed.

include_once

PHP also has another very similar function to the include construct - include_once.

Although both work nearly identically, there is a key difference in that the include_once construct prevents the same file being included more than once. The include construct on the other hand will overwrite the original include.

Similar functions

There also exists a require construct and a require_once construct. Both of these constructs work exactly the same way as the include constructs except that when an error occurs, instead of throwing a standard PHP warning, they throw a compile error thus stopping script execution.