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<td><h1>CodeIgniter User Guide Version 2.1.3</h1></td>
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<p>Controllers are the heart of your application, as they determine how HTTP requests should be handled.</p>
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<li><a href="#what">What is a Controller?</a></li>
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<li><a href="#hello">Hello World</a></li>
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<li><a href="#functions">Functions</a></li>
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<li><a href="#passinguri">Passing URI Segments to Your Functions</a></li>
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<li><a href="#default">Defining a Default Controller</a></li>
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<li><a href="#remapping">Remapping Function Calls</a></li>
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<li><a href="#output">Controlling Output Data</a></li>
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<li><a href="#private">Private Functions</a></li>
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<li><a href="#subfolders">Organizing Controllers into Sub-folders</a></li>
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<li><a href="#constructors">Class Constructors</a></li>
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<li><a href="#reserved">Reserved Function Names</a></li>
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<h2>What is a Controller?</h2>
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<p><dfn>A Controller is simply a class file that is named in a way that can be associated with a URI.</dfn></p>
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<p>Consider this URI:</p>
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<code>example.com/index.php/<var>blog</var>/</code>
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<p>In the above example, CodeIgniter would attempt to find a controller named <dfn>blog.php</dfn> and load it.</p>
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<p><strong>When a controller's name matches the first segment of a URI, it will be loaded.</strong></p>
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<h2>Let's try it: Hello World!</h2>
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<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>
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<textarea class="textarea" style="width:100%" cols="50" rows="10">
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class Blog extends CI_Controller {
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public function index()
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<p>Then save the file to your <dfn>application/controllers/</dfn> folder.</p>
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<p>Now visit the your site using a URL similar to this:</p>
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<code>example.com/index.php/<var>blog</var>/</code>
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<p>If you did it right, you should see <samp>Hello World!</samp>.</p>
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<p>Note: Class names must start with an uppercase letter. In other words, this is valid:</p>
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class <var>Blog</var> extends CI_Controller {<br />
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<p>This is <strong>not</strong> valid:</p>
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class <var>blog</var> extends CI_Controller {<br />
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<p>Also, always make sure your controller <dfn>extends</dfn> the parent controller class so that it can inherit all its functions.</p>
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<a name="functions"></a>
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<p>In the above example the function name is <dfn>index()</dfn>. The "index" function is always loaded by default if the
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<strong>second segment</strong> of the URI is empty. Another way to show your "Hello World" message would be this:</p>
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<code>example.com/index.php/<var>blog</var>/<samp>index</samp>/</code>
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<p><strong>The second segment of the URI determines which function in the controller gets called.</strong></p>
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<p>Let's try it. Add a new function to your controller:</p>
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<textarea class="textarea" style="width:100%" cols="50" rows="15">
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class Blog extends CI_Controller {
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public function index()
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public function comments()
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echo 'Look at this!';
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<p>Now load the following URL to see the <dfn>comment</dfn> function:</p>
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<code>example.com/index.php/<var>blog</var>/<samp>comments</samp>/</code>
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<p>You should see your new message.</p>
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<a name="passinguri"></a>
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<h2>Passing URI Segments to your Functions</h2>
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<p>If your URI contains more then two segments they will be passed to your function as parameters.</p>
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<p>For example, lets say you have a URI like this:</p>
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<code>example.com/index.php/<var>products</var>/<samp>shoes</samp>/<kbd>sandals</kbd>/<dfn>123</dfn></code>
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<p>Your function will be passed URI segments 3 and 4 ("sandals" and "123"):</p>
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class Products extends CI_Controller {<br />
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public function shoes($sandals, $id)<br />
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{<br />
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echo $sandals;<br />
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echo $id;<br />
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}<br />
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<p class="important"><strong>Important:</strong> If you are using the <a href="routing.html">URI Routing</a> feature, the segments
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passed to your function will be the re-routed ones.</p>
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<a name="default"></a>
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<h2>Defining a Default Controller</h2>
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<p>CodeIgniter can be told to load a default controller when a URI is not present,
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as will be the case when only your site root URL is requested. To specify a default controller, open
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your <dfn>application/config/routes.php</dfn> file and set this variable:</p>
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<code>$route['default_controller'] = '<var>Blog</var>';</code>
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<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
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specifying any URI segments you'll see your Hello World message by default.</p>
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<a name="remapping"></a>
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<h2>Remapping Function Calls</h2>
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<p>As noted above, the second segment of the URI typically determines which function in the controller gets called.
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CodeIgniter permits you to override this behavior through the use of the <kbd>_remap()</kbd> function:</p>
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<code>public function _remap()<br />
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// Some code here...<br />
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<p class="important"><strong>Important:</strong> If your controller contains a function named <kbd>_remap()</kbd>, it will <strong>always</strong>
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get called regardless of what your URI contains. It overrides the normal behavior in which the URI determines which function is called,
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allowing you to define your own function routing rules.</p>
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<p>The overridden function call (typically the second segment of the URI) will be passed as a parameter to the <kbd>_remap()</kbd> function:</p>
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<code>public function _remap(<var>$method</var>)<br />
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if ($method == 'some_method')<br />
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{<br />
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$this->$method();<br />
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}<br />
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else<br />
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{<br />
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$this->default_method();<br />
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}<br />
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<p>Any extra segments after the method name are passed into <kbd>_remap()</kbd> as an optional second parameter. This array can be used in combination with PHP's <a href="http://php.net/call_user_func_array">call_user_func_array</a> to emulate CodeIgniter's default behavior.</p>
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<code>public function _remap($method, $params = array())<br />
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$method = 'process_'.$method;<br />
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if (method_exists($this, $method))<br />
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{<br />
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return call_user_func_array(array($this, $method), $params);<br />
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}<br />
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show_404();<br />
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<a name="output"></a>
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<h2>Processing Output</h2>
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<p>CodeIgniter has an output class that takes care of sending your final rendered data to the web browser automatically. More information on this can be found in the
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<a href="views.html">Views</a> and <a href="../libraries/output.html">Output class</a> pages. In some cases, however, you might want to
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post-process the finalized data in some way and send it to the browser yourself. CodeIgniter permits you to
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add a function named <dfn>_output()</dfn> to your controller that will receive the finalized output data.</p>
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<p><strong>Important:</strong> If your controller contains a function named <kbd>_output()</kbd>, it will <strong>always</strong>
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be called by the output class instead of echoing the finalized data directly. The first parameter of the function will contain the finalized output.</p>
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<p>Here is an example:</p>
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public function _output($output)<br />
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echo $output;<br />
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<p class="important">Please note that your <dfn>_output()</dfn> function will receive the data in its finalized state. Benchmark and memory usage data will be rendered,
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cache files written (if you have caching enabled), and headers will be sent (if you use that <a href="../libraries/output.html">feature</a>)
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before it is handed off to the _output() function.<br />
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To have your controller's output cached properly, its <dfn>_output()</dfn> method can use:<br />
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<code>if ($this->output->cache_expiration > 0)<br />
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$this->output->_write_cache($output);<br />
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If you are using this feature the page execution timer and memory usage stats might not be perfectly accurate
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since they will not take into acccount any further processing you do. For an alternate way to control output <em>before</em> any of the final processing is done, please see
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the available methods in the <a href="../libraries/output.html">Output Class</a>.</p>
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<a name="private"></a>
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<h2>Private Functions</h2>
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<p>In some cases you may want certain functions hidden from public access. To make a function private, simply add an
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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>
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private function _utility()<br />
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// some code<br />
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<p>Trying to access it via the URL, like this, will not work:</p>
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<code>example.com/index.php/<var>blog</var>/<samp>_utility</samp>/</code>
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<a name="subfolders"></a>
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<h2>Organizing Your Controllers into Sub-folders</h2>
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<p>If you are building a large application you might find it convenient to organize your controllers into sub-folders. CodeIgniter permits you to do this.</p>
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<p>Simply create folders within your <dfn>application/controllers</dfn> directory and place your controller classes within them.</p>
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<p><strong>Note:</strong> When using this feature the first segment of your URI must specify the folder. For example, lets say you have a controller
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<code>application/controllers/<kbd>products</kbd>/shoes.php</code>
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<p>To call the above controller your URI will look something like this:</p>
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<code>example.com/index.php/products/shoes/show/123</code>
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<p>Each of your sub-folders may contain a default controller which will be
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called if the URL contains only the sub-folder. Simply name your default controller as specified in your
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<dfn>application/config/routes.php</dfn> file</p>
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<p>CodeIgniter also permits you to remap your URIs using its <a href="routing.html">URI Routing</a> feature.</p>
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<h2><a name="constructors"></a>Class Constructors</h2>
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<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>
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<code>parent::__construct();</code>
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<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>
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class <kbd>Blog</kbd> extends CI_Controller {<br />
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public function <kbd>__construct()</kbd><br />
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{<br />
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<var>parent::__construct();</var><br />
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// Your own constructor code<br />
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}<br />
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<p>Constructors are useful if you need to set some default values, or run a default process when your class is instantiated.
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Constructors can't return a value, but they can do some default work.</p>
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<a name="reserved"></a>
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<h2>Reserved Function Names</h2>
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<p>Since your controller classes will extend the main application controller you
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must be careful not to name your functions identically to the ones used by that class, otherwise your local functions
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will override them. See <a href="reserved_names.html">Reserved Names</a> for a full list.</p>
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<p>That, in a nutshell, is all there is to know about controllers.</p>
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