Error handling is very important in any application. In CodeIgniter, error handling helps developers to:

• Find issues in code.
• Show user-friendly error messages.
• Log errors for debugging later.

CodeIgniter provides multiple ways to handle errors, such as error reporting levels, error logging, exceptions, and custom error messages.

🔹 Step 1: Error Reporting Levels

In application/config/config.php, you can set the environment mode.

define('ENVIRONMENT', 'development');

• development → Shows all errors (good for debugging).
• testing → Limited error reporting.
• production → Hides sensitive errors from users.

👉 In index.php, you’ll see something like:

switch (ENVIRONMENT) {
    case 'development':
        error_reporting(-1);
        ini_set('display_errors', 1);
    break;

    case 'production':
        error_reporting(0);
        ini_set('display_errors', 0);
    break;
}

🔹 Step 2: Showing Error Messages

Use CodeIgniter’s show_error() function:

if (!$user) {
    show_error("User not found!", 404, "An Error Was Encountered");
}

Parameters:

1. Message → "User not found!"
2. Status Code → 404 (Not Found)
3. Heading → "An Error Was Encountered"

🔹 Step 3: Showing 404 Error

When a page is not found, you can use:

show_404();

Example:

public function view($page = 'home')
{
    if (!file_exists(APPPATH . 'views/pages/' . $page . '.php')) {
        show_404();  // Show custom 404 page
    }

    $this->load->view('pages/' . $page);
}

🔹 Step 4: Error Logging

CodeIgniter can log errors automatically.

In application/config/config.php:

$config['log_threshold'] = 1;

Log levels:

• 0 = No logging
• 1 = Error messages
• 2 = Debug messages
• 3 = Informational messages
• 4 = All messages

👉 Logs are stored in:

application/logs/log-YYYY-MM-DD.php

Example of writing custom log:

log_message('error', 'Something went wrong!');
log_message('debug', 'Debugging message');
log_message('info', 'Just some information');

🔹 Step 5: Custom Error Pages

You can create a custom error page in:

application/views/errors/html/error_404.php
application/views/errors/html/error_general.php

Example error_404.php:

<h1>Oops! Page not found.</h1>
<p>The page you are looking for might have been removed.</p>
<a href="<?= base_url(); ?>">Go Back Home</a>

🔹 Step 6: Handling PHP Exceptions

You can use try-catch blocks in controllers or models:

try {
    $this->db->query("INVALID SQL QUERY");
} catch (Exception $e) {
    log_message('error', $e->getMessage());
    show_error("Database error occurred!");
}