There are n number of situation where we want to call a function before or after an action. In Codeigniter, we can implement this by using Hooks. In-other-word, we can say Hooks are the event which can be called before or after the execution of an event.

Steps for writing Hooks: We have to write few steps for implementing hooks in Codeigniter.

Step 1: First we want to enable hooks after changing the file  application/config/config.php.

    $config['enable_hooks'] = FALSE;
    // Change this statement to true
    $config['enable_hooks'] = TRUE;

Step 2: Now we will create a controller Codeigniter/application/controllers/User.php" with below code::

    <?php
    defined('BASEPATH') OR exit('No direct script access allowed');
    class User extends CI_Controller {
        function index(){
            echo "Welcome to our site";
        }
    }
    ?>

Step 3: Now we will create a file "application/hooks/Hookcall.php" and save this on below path ::

    <?php
    defined('BASEPATH') OR exit('No direct script access allowed');
    class Hookcall extends CI_Controller {
        public function hookevent(){
            echo "Good Morning, Everyone";
        }
    }
    ?>

Step 4: Now we will go to the "Codeigniter/application/config/hooks.php" and do the following operation on that

$hook['pre_controller'] = array(
                                'class'    => 'Hookcall',
                                'function' => 'hookevent',
                                'filename' => 'Hookcall.php',
                                'filepath' => 'hooks'
                                );

Note: We can also do multiple calls to the same hook.Below is the code:

$hook['pre_controller'][] = array(
                                'class'    => 'Hookcall',
                                'function' => 'hookevent',
                                'filename' => 'Hookcall.php',
                                'filepath' => 'hooks'
                                );
$hook['pre_controller'][] = array(
                                'class'    => 'Hook_othercall',
                                'function' => 'hook_otherevent',
                                'filename' => 'Hook_othercall.php',
                                'filepath' => 'hooks'
                                );

By this way, we will implement hooks in Codeigniter.