# CodeIgniter User Guide Version 1.7.3

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# CodeIgniter at a Glance

## CodeIgniter is an Application Framework

CodeIgniter is a toolkit for people who build web application using PHP. Its goal is to enable you to develop projects much faster than you could if you were writing code from scratch, by providing a rich set of libraries for commonly needed tasks, as well as a simple interface and logical structure to access these libraries. CodeIgniter lets you creatively focus on your project by minimizing the amount of code needed for a given task.

## CodeIgniter is Free

CodeIgniter is licensed under an Apache/BSD-style open source license so you can use it however you please. For more information please read the license agreement.

## CodeIgniter Runs on PHP 4

CodeIgniter is written to be compatible with PHP 4. Although we would have loved to take advantage of the better object handling in PHP 5 since it would have simplified some things we had to find creative solutions for (looking your way, multiple inheritance), at the time of this writing PHP 5 is not in widespread use, which means we would be alienating most of our potential audience. Major OS vendors like RedHat are moving slowly to support PHP 5, and they are unlikely to do so in the short term, so we felt that it did not serve the best interests of the PHP community to write CodeIgniter in PHP 5.

Note: CodeIgniter will run on PHP 5. It simply does not take advantage of any native features that are only available in that version.

## CodeIgniter is Light Weight

Truly light weight. The core system requires only a few very small libraries. This is in stark contrast to many frameworks that require significantly more resources. Additional libraries are loaded dynamically upon request, based on your needs for a given process, so the base system is very lean and quite fast.

## CodeIgniter is Fast

Really fast. We challenge you to find a framework that has better performance than CodeIgniter.

## CodeIgniter Uses M-V-C

CodeIgniter uses the Model-View-Controller approach, which allows great separation between logic and presentation. This is particularly good for projects in which designers are working with your template files, as the code these file contain will be minimized. We describe MVC in more detail on its own page.

## CodeIgniter Generates Clean URLs

The URLs generated by CodeIgniter are clean and search-engine friendly. Rather than using the standard "query string" approach to URLs that is synonymous with dynamic systems, CodeIgniter uses a segment-based approach:

`example.com/news/article/`345``

Note: By default the index.php file is included in the URL but it can be removed using a simple .htaccess file.

## CodeIgniter Packs a Punch

CodeIgniter comes with full-range of libraries that enable the most commonly needed web development tasks, like accessing a database, sending email, validating form data, maintaining sessions, manipulating images, working with XML-RPC data and much more.

## CodeIgniter is Extensible

The system can be easily extended through the use of plugins and helper libraries, or through class extensions or system hooks.

## CodeIgniter Does Not Require a Template Engine

Although CodeIgniter does come with a simple template parser that can be optionally used, it does not force you to use one. Template engines simply can not match the performance of native PHP, and the syntax that must be learned to use a template engine is usually only marginally easier than learning the basics of PHP. Consider this block of PHP code:

`<ul>
<?php foreach ($addressbook as $name):?>
<li><?=$name?></li>
<?php endforeach; ?>
</ul>`

Contrast this with the pseudo-code used by a template engine:

`<ul>
{foreach from=$addressbook item="name"}
<li>{$name}</li>
{/foreach}
</ul>`

Yes, the template engine example is a bit cleaner, but it comes at the price of performance, as the pseudo-code must be converted back into PHP to run. Since one of our goals is maximum performance, we opted to not require the use of a template engine.

## CodeIgniter is Thoroughly Documented

Programmers love to code and hate to write documentation. We're no different, of course, but since documentation is as important as the code itself, we are committed to doing it. Our source code is extremely clean and well commented as well.

## CodeIgniter has a Friendly Community of Users

Our growing community of users can be seen actively participating in our Community Forums.