Top CodeIgniter Interview Questions 2025 - Beginner to Advanced

1. How can you create a custom library in CodeIgniter?

Explanation:
A custom library is useful when you want to encapsulate reusable logic.

Example: Create: application/libraries/My_library.php

class My_library {     public function greet($name) {         return "Hello, " . $name;     } }

Load it in controller:

$this->load->library('my_library'); echo $this->my_library->greet('Developer');

2. How do you implement CSRF protection in CodeIgniter manually in an API context?

Explanation:
CSRF is enabled in config/config.php. For APIs, you might want to handle it manually.

$config['csrf_protection'] = TRUE;

In views:

<input type="hidden" name="<?=$this->security->get_csrf_token_name();?>"  value="<?=$this->security->get_csrf_hash();?>" />

3. Explain the use of base_url() and site_url() with differences.

Explanation:

• base_url() returns the root URL of your site.

• site_url() generates a complete URL using routing.

Example:

echo base_url('assets/css/style.css'); echo site_url('user/profile');

4. How do you create REST APIs in CodeIgniter?

Explanation:
Use the CodeIgniter REST Server library (e.g., by Chris Kacerguis).

Example (Controller method):

public function users_get() {     $users = $this->User_model->get_all();     $this->response($users, REST_Controller::HTTP_OK); }

5. How do you prevent SQL injection in CodeIgniter?

Explanation:
Use Active Record or Query Bindings.

Example:

$this->db->where('email', $email); $query = $this->db->get('users'); // OR $sql = "SELECT * FROM users WHERE email = ?"; $query = $this->db->query($sql, array($email));

6. How to use Middleware (like Laravel) in CodeIgniter?

Explanation:
Though not native in CodeIgniter 3, you can simulate middleware using Hooks or base controllers.

Example (Base controller check):

class MY_Controller extends CI_Controller {     public function __construct() {         parent::__construct();         // Simulate middleware         if (!$this->session->userdata('logged_in')) {             redirect('login');         }     } }

7. How do you handle multi-language support in CodeIgniter?

Explanation:
CodeIgniter provides language library.

Example:

// Load language $this->lang->load('message', 'french'); // Access language line echo $this->lang->line('welcome');

8. How to implement HMVC (Hierarchical MVC) in CodeIgniter?

Explanation:
You can implement HMVC using the MX_Controller by loading a modular extension package.

Steps:

1. Download CodeIgniter HMVC package

2. Extend controllers from MX_Controller

3. Use Modules::run('module/function')

9. How do you cache query results in CodeIgniter?

Explanation:
Enable caching in database.php and use cache_on:

$this->db->cache_on(); $query = $this->db->get('users'); $this->db->cache_off();

Also supports file-based page caching:

$this->output->cache(10); // Cache for 10 minutes

10. How to handle 404 errors and create a custom error page in CodeIgniter?

Explanation:
Customize the 404 override in routes.php:

$route['404_override'] = 'errors/page_missing';

Create a controller and view for Errors/page_missing to show a user-friendly 404 page.

11. How do you use transactions in CodeIgniter to ensure data integrity?

Explanation:
CodeIgniter supports database transactions to handle operations like inserts/updates/deletes securely.

Example:

$this->db->trans_start(); $this->db->insert('orders', $order_data); $this->db->insert('order_items', $item_data); $this->db->trans_complete(); if ($this->db->trans_status() === FALSE) {     // Rollback happened }

12. How can you use environment-based configuration in CodeIgniter?

Explanation:
Use different config files or logic for development, testing, and production.

Steps:

1. Set environment in index.php:

       define('ENVIRONMENT', 'development');

2. In config:

 if (ENVIRONMENT == 'development') {     $config['base_url'] = 'http://localhost/'; } else {    $config['base_url'] = 'https://production.com/'; }

13. How do you integrate a third-party PHP library in CodeIgniter?

Explanation:
Use application/libraries/ or use Composer.

Example:

require_once(APPPATH.'third_party/SomeLibrary.php'); $lib = new SomeLibrary();

Or via Composer:

composer require guzzlehttp/guzzle

Then autoload using:

require_once APPPATH . '../vendor/autoload.php';

14. How do you handle file uploads securely in CodeIgniter?

Explanation:
Use CodeIgniter’s file upload library and validate file type, size, and name.

Example:

$config['upload_path'] = './uploads/'; $config['allowed_types'] = 'jpg|png|gif'; $config['max_size'] = 2048; $this->load->library('upload', $config); if ($this->upload->do_upload('profile_pic')) {     $data = $this->upload->data(); } else {     echo $this->upload->display_errors(); }

15. How do you prevent direct script access in CodeIgniter?

Explanation:
By using:

defined('BASEPATH') OR exit('No direct script access allowed');

This ensures scripts run only via the CI controller.

16. How do you create pagination in CodeIgniter?

Explanation:
Use the pagination library and configure base URL, total rows, and per page.

Example:

$this->load->library('pagination'); $config['base_url'] = base_url('users/index'); $config['total_rows'] = $this->db->count_all('users'); $config['per_page'] = 10; $this->pagination->initialize($config); $data['users'] = $this->User_model->get_users($config['per_page'], $this->uri->segment(3));

17. How do you use .env files or environment variables in CodeIgniter 4?

Explanation:
In CI4, .env file allows secure environment-based configuration.

Example (.env):

app.baseURL = 'http://localhost:8080/' database.default.username = root

Then in code:

$db_user = getenv('database.default.username');

18. How to implement user authentication from scratch in CodeIgniter?

Explanation:
Use session-based login system.

Example:

// Login Controller if ($this->input->post()) {     $user = $this->User_model->check_credentials($email, $password);     if ($user) {         $this->session->set_userdata('user_id', $user->id);         redirect('dashboard');     } else {         $this->session->set_flashdata('error', 'Invalid login');     } }

19. How to use AJAX with CodeIgniter for real-time form submission?

Explanation:
Send AJAX requests to CodeIgniter controller methods and return JSON.

JavaScript Example:

$.post("user/submit_form", {name: "John"}, function(response) {     alert(response.status); }, 'json');

CodeIgniter Controller:

public function submit_form() {     $name = $this->input->post('name');     echo json_encode(['status' => 'success', 'name' => $name]); }

20. How can you load multiple views inside a layout in CodeIgniter?

Explanation:
Create a layout view and load partials from controller.

Example:

// Controller $data['main_content'] = 'pages/about'; $this->load->view('layout', $data);

In layout view:

<!DOCTYPE html> <html> <head><title>My Site</title></head> <body> <?php $this->load->view($main_content); ?> </body> </html>