Upgrade CodeIgniter 3 to PHP 8: Fix Deprecation Errors Instantly with AI

If you are managing a legacy project built on CodeIgniter 3, you are likely facing a dilemma. Hosting providers are forcing upgrades to PHP 8.0, 8.1, or 8.2, but your application was built for PHP 5 or 7.

When you switch the PHP version, your site probably greets you with:

"Fatal Error: Array and string offset access syntax with curly braces is no longer supported" or "Deprecated: Required parameter follows optional parameter".

Rewriting the whole app to Laravel or CI4 takes months. In this guide, I will show you how to use AI to refactor your CI3 code for PHP 8 compatibility in minutes, not months.

PHP 7.4 is EOL. Learn how to run CodeIgniter 3 on PHP 8.2 by using AI to fix common "Deprecated" errors and syntax mismatches without rewriting the whole app

The Big 3 Killers in PHP 8

PHP 8 is much stricter than PHP 7. AI can spot these issues faster than your eyes can.

1. The "Curly Brace" Syntax

In the old days, we accessed array offsets like this: $array{0}. In PHP 8, this crashes the site. You must use square brackets $array[0].

The Prompt:

Prompt:
"I am upgrading to PHP 8. Scan this PHP code snippet and identify any syntax that is removed or deprecated in PHP 8 (like curly braces for arrays). Rewrite the code to be PHP 8.2 compatible."

2. Optional Parameters Before Required Ones

This is the most common error in CodeIgniter libraries.
Invalid in PHP 8: function test($a = [], $b)
Valid: function test($b, $a = [])

Fixing this manually in 100 files is painful. Just paste your Controller or Model into AI and ask:

"Fix the method signatures in this class to comply with PHP 8 'Optional Parameter' rules."

3. Real World Case: Fixing a CI3 Model

Let's say you have an old Model that throws errors. Don't guess. Let AI do the heavy lifting.

Prompt Strategy:

Act as a Senior PHP Developer.
Here is a CodeIgniter 3 Model written in 2017:
[PASTE CODE HERE]

Refactor this code to run on PHP 8.2.
1. Fix constructor syntax (__construct).
2. Fix any 'Array to String' conversions.
3. Ensure null safety checks are added.

The AI Result (Example):

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

class User_model extends CI_Model {

    public function __construct() {
        parent::__construct();
        // AI ensures the parent constructor is called correctly
    }

    public function get_user($id) {
        // PHP 8 Warning fix: Check if ID is numeric
        if (!is_numeric($id)) {
            return null;
        }
        
        $query = $this->db->get_where('users', ['id' => $id]);
        return $query->row_array() ?? []; // Null coalescing operator (PHP 7+)
    }
}
?>

Pro Tip: The "Rector" Alternative

If you have a massive project, you can ask AI to help you configure a tool called Rector. Rector can automatically upgrade your code. And you can solve error with AI like error on this image.