This tutorial will show you how to divide your code into more files and how to include various files into your actual PHP code. Maintain organization and ease of updates using file includes.

PHP include file

Step 1 - Include files introduction

If you want to make a project then it is not a good idea to put all of the code into one file. Even a quite simple task can result a huge amount of code. To maintain and reuse a code from a single file is quite hard.

If you download and check the source code of any PHP project you will find a lot of files. Each file contains only a well defined task implementation. For example in OOP each class has it's own file or you create a file for DB management an other one for mail sending and an other to display menu system.

A real example could be a project with the following files:

• index.php
• header.php
• footer.php
• menu.php
• content.php

• include
• require
• include_once
• require_once

In the next steps I will explain how to use them.

Step 2 - The php include function

The first way to include a file is using the include function. This is a PHP built in code and the synatx is the following:

include ( filename )

This code tries to include the content of the file defined by filename. If the file doesn't exists the include function will report a warning but the script will continue.

Let's see an example. First we create a file which will be included later and it only contains a variable initialisation:

Code: internal.php


	

	

	<?php
	
	
	

	

	   $i = 100;
	
	
	

	

	?>
	
	

Code: test.php


	

	

	<?php
	
	
	

	

	  echo "Value of i before include is: -$i-<br/>";
	
	
	

	

	   include("internal.php");
	
	
	

	

	 echo "Value of i after include is: -$i-<br/>";
	
	
	

	

	?>
	
	

Output: 

Value of i before include is: -- 
Value of i after include is: -100-  

Code: 


	

	

	<?php
	
	
	

	

	  echo "Value of i before include is: -$i-<br/>";
	
	
	

	

	   $i=100;
	
	
	

	

	  echo "Value of i after include is: -$i-<br/>";
	
	
	

	

	?>
	
	

Of course in a real life application your files contains a bit more code :)

Step 3 - Include file more than once

Sometimes it can happen that you want to include a file in your script more than once. There is no problem with it. You can do this by calling include more times. Altough in such case maybe a well organized loop can be better.

So to demonstarte more include calls I have created the following example code:

Code: internal.php 


	

	

	<?php
	
	
	

	

	  echo "-->internal.php<--<br/>";
	
	
	

	

	?>
	
	

Code: 


	

	

	<?php
	
	
	

	

	   include ('internal.php');
	
	
	

	

	   echo "Multiple include test.<br/>";
	
	
	

	

	   include ('internal.php');
	
	
	

	

	  echo "Now include it again.<br/>";
	
	
	

	

	   include ('internal.php');
	
	
	

	

	  echo "And again.<br/>";
	
	
	

	

	   include ('internal.php');
	
	
	

	

	?>
	
	

Output: 

-->internal.php<-- Multiple include test. -->internal.php

<-- Now include it again. -->internal.php<-- And again. -->internal.php<--   

Step 4 - The php require function

In a lot of cases it is very important to have the file really included in our code. For example if the include of a database management code fails and the script continue it's run then it will cause a lot of unwanted error in the later steps. To avoid this you can say if the include was not success then stop all the further activity. For this purpose was the function require() introduced.

The usage if php require function is quite similar to the include however if the file can not be found require will report a fatal error and the script will die.

Let's see an example:

Code: 


	

	

	<?php
	
	
	

	

	 echo "Try to include wrong file first with include.<br/>";
	
	
	

	

	   include ('internalwrong.php');
	
	
	

	

	  echo "Now try it with require.<br/>";
	
	
	

	

	   require ('internalwrong.php');
	
	
	

	

	  echo "Finish.";
	
	
	

	

	?>
	
	

Output: 

Try to include wrong file first with include.
 
Warning: include(internalwrong.php) [function.include]: failed to open stream: No such file or directory in Z:WorkWebSitestestf1test.php on line 3
 
Warning: include() [function.include]: Failed opening 'internalwrong.php' for inclusion (include_path='D:Program FilesZendZendStudio-5.5.0binZendFrameworklibrary') in Z:WorkWebSitestestf1test.php on line 3
Now try it with require.
 
Warning: require(internalwrong.php) [function.require]: failed to open stream: No such file or directory in Z:WorkWebSitestestf1test.php on line 5
 
Fatal error: require() [function.require]: Failed opening required 'internalwrong.php'

Step 5 - Include files only once

In a big and complaex project it can happen that you don't know whether a file was included yet or not. For example suppose the following situation:

• A.php includes B.php
• B.php includes C.php only if a condition is true in B.php

In this case you can not be sure that C.php is surely included in A.php besides this you want to avoid duplicated includes. To solve this problem you can use the include_once or the require_once functions.

These functions first checks whether a file was included or not. After this check they include the file only if it was not included before. To demonstarte this let's go back to an older example and now use include_once instead of include as follows:

Code: 


	

	

	<?php
	
	
	

	

	   include_once ('internal.php');
	
	
	

	

	  echo"Multiple include test.<br/>";
	
	
	

	

	   include_once ('internal.php');
	
	
	

	

	  echo"Now include it again.<br/>";
	
	
	

	

	   include_once ('internal.php');
	
	
	

	

	  echo "Multiple include test.<br/>";
	
	
	

	

	   include_once ('internal.php');
	
	
	

	

	?>