CodeIgniter 3 not calling default controller?

Question

I have been asked to look into an issue where the default_controller in a CodeIgniter 3 project does not seem to be called. Instead we are seeing a 404 error.

In the application/controllers folder there is a Welcome.php file with the following content:

class Welcome extends CI_Controller {

        public function __construct()
        {
                parent::__construct();
                // Your own constructor code
        }

        public function index()
        {
                print('hello');
                $this->load->view('welcome_message');
        }
}

The application/config/routes.php file has:

$route['default_controller'] = "welcome";

I only see a 404 and none of the expected text.

Adding a print statement to the routes.php shows that it is being loaded. Also, tying it explicitly to a route has it called, but not when it is set to be the default controller.

$route['blah'] = "welcome"

Can anyone suggest what may be going on?

BTW We are using PHP7 on an Ubuntu 16.04 machine.

Answer 1

Turns out the project was an upgrade from a CodeIgniter 2 project and there were some migration steps that hadn't quite been completed. It turned out that there was a MY_Router.php in the libraries folder, that seemed to be throwing things off - at least moving it into applications/core solved the issue.

An additional modification was needed in the MY_Router.php file given the capitalization of the filenames, requested as part of the CI3 migration:

function _validate_request($segments)
{
    // Does the requested controller exist in the root folder?
    if (file_exists(APPPATH.'controllers/'.ucfirst($segments[0]).'.php'))
    {
        return $segments;
    }
    ...
}

BTW I was sure it wasn't a HTTP server rewrite issue, since a CodeIgniter 404 error page was showing the expected call path. I had added a print(_SERVER['REQUEST_URI']) to see what was going on.

Edit: I now see that ucfirst approach above is not ideal in other installations, but given that there are no subfolders in this project's controllers folder, it is a quick fix for this project.