CodeIgniter: Installation

CodeIgniter is a lightweight PHP framework known for its small footprint and clear documentation.

This guide covers CodeIgniter: Installation with working code you can adapt for your own projects. We will walk through the setup, show what the code actually does at each step, and flag the spots where things tend to break.

If you have worked with CodeIgniter before, skip ahead to the code examples. If this is your first time, read the whole thing - the order matters.

How It Works

// application/controllers/Welcome.php
<?php
defined('BASEPATH') OR exit('No direct script access allowed');

class Welcome extends CI_Controller {
    public function index()
    {
        $data['title'] = 'Welcome to CodeIgniter';
        $this->load->view('header', $data);
        $this->load->view('welcome_message', $data);
        $this->load->view('footer');
    }
}

The key idea here: get something running first, then refine. The code above is intentionally minimal so you can see the structure without noise.

Step-by-Step Walkthrough

1. Set up your environment. Make sure your PHP version matches what the framework or library expects. Run php -v to check.
2. Create the base files. Copy the example above into your project directory. Adjust the connection details or paths to match your local setup.
3. Test immediately. Do not write 200 lines before running the code. Test after every meaningful change. This habit catches typos and config errors before they compound.
4. Read the error messages. PHP error messages are verbose for a reason. The file path and line number in the error output will point you to the problem 90% of the time.
5. Refactor once it works. Move hardcoded values into configuration. Extract repeated logic into functions. But only after the basic version runs.

Working with the Code

There are a few things to keep in mind when adapting this for production:

• Error handling is not optional. The examples here use basic try/catch blocks. In production, log errors and show generic messages to users.
• Input validation goes before everything else. If the data comes from a user, treat it as hostile until proven otherwise.
• File paths differ between OS environments. Use the appropriate directory separator or PHP constants like DIRECTORY_SEPARATOR when building paths.

Common Mistakes

• Not checking return values. Functions that fail silently are the hardest bugs to track. Always check what comes back.
• Skipping error reporting during development. Set error_reporting(E_ALL) and display_errors = On locally. Turn display off in production but keep logging on.
• Hardcoding credentials. Even in tutorials, get in the habit of using environment variables or a config file outside the web root.
• Ignoring character encoding. Use UTF-8 everywhere: database, connection string, HTML meta tag. Mismatched encodings cause garbled text that is painful to debug later.
• Copy-pasting without reading. Seriously - read the code before you run it. One wrong table name or missing semicolon will cost you thirty minutes of confusion.

Frequently Asked Questions

Why does CodeIgniter show a 404 for my controller?

Check that the filename matches the class name (case-sensitive on Linux). Also verify your routes.php does not override the default routing.

How do I load a model in CodeIgniter?

Use $this->load->model("Model_name") in your controller. The model file goes in application/models/.

Can I use CodeIgniter 3 with PHP 8?

CodeIgniter 3 has compatibility issues with PHP 8.0+. Use CodeIgniter 4 for PHP 8 projects, or apply the community patches for CI3.