Error Handling and Logging in CodeIgniter (CodeIgniter 4)

CodeIgniter 4 provides a robust error handling and logging system that helps you debug during development and monitor issues in production.

1. Environment-Based Error Handling

CodeIgniter behaves differently based on environment mode.

Set Environment

In .env:

CI_ENVIRONMENT = development

2. Error Configuration Files

Main Error Config

app/Config/Exceptions.php

Controls:

• Error views

• Logging behavior

• Custom exception handling

3. Display Errors (Development Only)

In app/Config/App.php:

public $displayErrors = true;

⚠️ Disable in production.

4. Error Views

Location:

app/Views/errors/

Examples:

• error_404.php

• error_exception.php

You can customize these pages.

5. Throwing Custom Errors

throw new \Exception('Something went wrong');

Or:

throw new \CodeIgniter\Exceptions\PageNotFoundException();

6. Logging System

Log Location

writable/logs/

Logging Levels

CodeIgniter supports PSR-3 log levels:

• emergency

• alert

• critical

• error

• warning

• notice

• info

• debug

Writing Logs

log_message('error', 'Database connection failed');
log_message('info', 'User logged in');

7. Log Configuration

File:

app/Config/Logger.php

Key settings:

public $threshold = 4; // Log everything up to error

8. Database Error Logging

Enable DB debug (development only):

'DBDebug' => true,

Disable in production to avoid sensitive info leaks.

9. Handling 404 Errors

$routes->set404Override(function () {
    return view('errors/custom_404');
});

10. Try–Catch Exception Handling

try {
    // risky code
} catch (\Throwable $e) {
    log_message('error', $e->getMessage());
    return redirect()->back()->with('error', 'Something went wrong');
}

11. Custom Error Controller

class ErrorController extends BaseController
{
    public function show404()
    {
        return view('errors/custom_404');
    }
}

12. Production Best Practices

✅ Disable detailed error display
✅ Enable logging
✅ Monitor logs regularly
❌ Never expose stack traces to users

Summary

• Environment-based error handling

• Built-in logging with PSR-3 support

• Custom error pages & exceptions

• Essential for debugging & security