CodeIgniter: checking if user logged in for multiple pages

I have a controller, which maps to section of my site and all of the pages within it (methods) should only appear if the user is logged in. Otherwise they should be redirected back to a login screen.

To get it working I've just done this:

function index() {

    if ($this->session->userdata('logged_in')) {
        $this->load->view('main');

    } else {
        redirect('/login');
    }
}

function archive() {

    if ($this->session->userdata('logged_in')) {

and so on... repeating that check in each method. What's the simplest way of doing this check once for multiple-or-all methods in the controller?

You can run code in every method of a Controller by running it in the __construct() method:

function __construct()
{
    parent::__construct();
    if ( ! $this->session->userdata('logged_in'))
    { 
        // Allow some methods?
        $allowed = array(
            'some_method_in_this_controller',
            'other_method_in_this_controller',
        );
        if ( ! in_array($this->router->fetch_method(), $allowed)
        {
            redirect('login');
        }
    }
}

You can remove the "allowed" bits if you want to restrict access to the whole thing, but there are better ways to do this, like creating a base controller:

// Create file application/core/MY_Controller.php
class Auth_Controller extends CI_Controller {

    function __construct()
    {
        parent::__construct();
        if ( ! $this->session->userdata('logged_in'))
        { 
            redirect('login');
        }
    }
}

Then have your restricted controllers extend Auth_Controller instead of CI_Controller. Now your code will be run every time the controller is loaded.

More info on extending core classes: http://www.codeigniter.com/user_guide/general/core_classes.html#extending-core-class

Also of interest: http://php.net/manual/en/language.oop5.decon.php