php - Extending base_url() to base_url_admin() not working properly in CodeIgniter

My config config_backend.php (autoloaded) looks like this:

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

$config['my_admin_url'] = 'admin';
Copy code

My helper admin_helper.php looks like this:

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

function base_url_admin()
{
    $ci =& get_instance();

    $ci->config->load('config_backend');
    $ci->load->helper('url');

    return base_url().$my_admin_url.'/';
}
Copy code

My code in the view looks like this:

<a href="<?php echo base_url_admin(); ?>">Admin</a>
Copy code

But the problem is that instead of the correct output like:

<a href="http://localhost/admin">Admin</a>
Copy code

The link looks like:

<a href="http://localhost">Admin</a>
Copy code

Funny thing is that when I do in helper e.g. this:

function base_url_admin()
{
    $ci =& get_instance();

    $ci->config->load('config_backend');
    $ci->load->helper('url');

    return "idiot";
}
Copy code

it outputs something like:

http://localhost/admin/idiot
Copy code

So, I assume that admin_helper is loaded, but I don't know how the admin appear there?

Any idea what am I doing wrong?