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<td><h1>Code Igniter User Guide Version 1.4.0</h1></td>
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Controllers
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<h1>Controllers</h1>
<p>Controllers are the heart of your application, as they determine how HTTP requests should be handled.</p>
<ul>
<li><a href="#what">What is a Controller?</a></li>
<li><a href="#hello">Hello World</a></li>
<li><a href="#functions">Functions</a></li>
<li><a href="#private">Private Functions</a></li>
<li><a href="#default">Defining a Default Controller</a></li>
<li><a href="#constructors">Class Constructors</a></li>
<li><a href="#reserved">Reserved Function Names</a></li>
</ul>
<a name="what"></a>
<h2>What is a Controller?</h2>
<p><dfn>A Controller is simply a class file that is named in a way that can be associated with a URI.</dfn></p>
<p>Consider this URI:</p>
<code>www.your-site.com/index.php/<var>blog</var>/</code>
<p>In the above example, Code Igniter would attempt to find a controller named <dfn>blog.php</dfn> and load it.</p>
<p><strong>When a controller's name matches the first segment of a URI, it will be loaded.</strong></p>
<a name="hello"></a>
<h2>Let's try it: Hello World!</h2>
<p>Let's create a simple controller so you can see it in action. Using your text editor, create a file called <dfn>blog.php</dfn>, and put the following code in it:</p>
<textarea class="textarea" style="width:100%" cols="50" rows="10">
<?php
class Blog extends Controller {
function index()
{
echo 'Hello World!';
}
}
?>
</textarea>
<p>Then save the file to your <dfn>application/controllers/</dfn> folder.</p>
<p>Now visit the your site using a URL similar to this:</p>
<code>www.your-site.com/index.php/<var>blog</var>/</code>
<p>If you did it right, you should see <samp>Hello World!</samp>.</p>
<p>Note: Class names must start with an uppercase letter. In other words, this is valid:
<code><?php<br />
class <var>Blog</var> extends Controller {<br />
<br />
}<br />
?></code>
<p>This is <strong>not</strong> valid:</p>
<code><?php<br />
class <var>blog</var> extends Controller {<br />
<br />
}<br />
?></code>
<p>Also, always make sure your controller <dfn>extends</dfn> the parent controller class so that it can inherit all its functions.</p>
<a name="functions"></a>
<h2>Functions</h2>
<p>In the above example the function name is <dfn>index()</dfn>. The "index" function is always loaded by default if the
<strong>second segment</strong> of the URI is empty. Another way to show your "Hello World" message would be this:</p>
<code>www.your-site.com/index.php/<var>blog</var>/<samp>index</samp>/</code>
<p><strong>The second segment of the URI determines which function in the controller gets called.</strong></p>
<p>Let's try it. Add a new function to your controller:</p>
<textarea class="textarea" style="width:100%" cols="50" rows="15">
<?php
class Blog extends Controller {
function index()
{
echo 'Hello World!';
}
function comments()
{
echo 'Look at this!';
}
}
?>
</textarea>
<p>Now load the following URL to see the <dfn>comment</dfn> function:</p>
<code>www.your-site.com/index.php/<var>blog</var>/<samp>comments</samp>/</code>
<p>You should see your new message.</p>
<a name="private"></a>
<h2>Private Functions</h2>
<p>In some cases you may not want certain functions accessible publicly. To make a function private, simply add an
underscore as the name prefix and it will not be served via a URL request. For example, if you were to have a function like this:</p>
<code>
function _utility()<br />
{<br />
// some code<br />
}</code>
<p>Trying to access it via the URL, like this, will not work:</p>
<code>www.your-site.com/index.php/<var>blog</var>/<samp>_utility</samp>/</code>
<a name="default"></a>
<h2>Defining a Default Controller</h2>
<p>Code Igniter can be told to load a default controller when a URI is not present,
as will be the case when only your site root URL is requested. To specify a default controller, open
your <dfn>application/config/routes.php</dfn> file and set this variable:</p>
<code>$route['default_controller'] = '<var>Blog</var>';</code>
<p>Where <var>Blog</var> is the name of the controller class you want used. If you now load your main index.php file without
specifying any URI segments you'll see your Hello World message by default.</p>
<a name="constructors"></a>
<h2>Class Constructors</h2>
<p>If you intend to use a constructor in any of your Controllers, you <strong>MUST</strong> place the following line of code in it:</p>
<code>parent::Controller();</code>
<p>The reason this line is necessary is because your local constructor will be overriding the one in the parent controller class so we need to manually call it.</p>
<p>If you are not familliar with constructors, in PHP 4, a <em>constructor</em> is simply a function that has the exact same name as the class:</p>
<code>
<?php<br />
class <kbd>Blog</kbd> extends Controller {<br />
<br />
function <kbd>Blog()</kbd><br />
{<br />
<var>parent::Controller();</var><br />
}<br />
}<br />
?></code>
<p>In PHP 5, constructors use the following syntax:</p>
<code>
<?php<br />
class <kbd>Blog</kbd> extends Controller {<br />
<br />
function <kbd>__construct()</kbd><br />
{<br />
<var>parent::Controller();</var><br />
}<br />
}<br />
?></code>
<p>Constructors are useful if you need to set some default values, or run a default process when your class is instantiated.
Constructors can't return a value, but they can do some default work.</p>
<a name="reserved"></a>
<h2>Reserved Function Names</h2>
<p>Since your controller classes will extend the main application controller you
must be careful not to name your functions identically to the ones used by that class, otherwise your local functions
will override them. The following
is a list of reserved names. Do not name your controller functions any of these:</p>
<ul>
<li>Controller</li>
<li>CI_Base</li>
<li>_ci_autoload</li>
<li>_ci_autoloader</li>
<li>_ci_assign_core</li>
<li>_ci_initialize</li>
<li>_ci_init_database</li>
<li>_ci_init_scaffolding</li>
<li>_ci_is_loaded</li>
<li>_ci_load</li>
<li>_ci_scaffolding</li>
<li>_ci_set_view_path</li>
</ul>
<p><br />If you are running PHP 4 there are some additional reserved names. These ONLY apply if you are running PHP 4.</p>
<ul>
<li>CI_Loader</li>
<li>config</li>
<li>database</li>
<li>file</li>
<li>helper</li>
<li>helpers</li>
<li>language</li>
<li>library</li>
<li>plugin</li>
<li>plugins</li>
<li>scaffolding</li>
<li>script</li>
<li>view</li>
<li>vars</li>
</ul>
<h2>That's it!</h2>
<p>That, in a nutshell, is all there is to know about controllers.</p>
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