difference between $this and $this->ci in codeigniter

hi i am using codeigniter , in my controller constructor sometimes i use $this sometimes $this->ci

in two constructors i have use like this

public function __construct()
{
    $this->ci =& get_instance();
    $this->ci->load->library('fo开发者_开发技巧rm_validation');
    $this->ci->load->library('catalog/CatalogManager');
}

function __construct() 
    {
    parent::__construct ();
    $this->ci = & get_instance ();
    $this->load->library ( 'auth_lib' );
    $this->load->library ( 'session' );
    }

when passing data to view i use

$this->ci->data and $this->data in above two cases .

neither gives errors , but i am confused , what is the correct use.

please help...........

All controllers extend the main CI_Controller, so calling something like $this->load means accessing the parent method load() inside the parent class CI_Controller.

$this->ci works because with $this->ci = &get_instance() you're calling a reference to the main controller class...again. If you look in the bootstrap file (IIRC. Or the codeigniter.php file) there's the function get_instance(), which does nothing but return (by reference) the instance of the CI_Controller class.

So, basically, calling $this->ci->load and $this->load are the same exact thing, only that the first is unnecessary within a Controller/Model/View because the system is already doing that in the parent class (through the method load).

If you have a look at libraries, for ex., you'll see instead that using $this->ci->method() is necessary, because you need to have available all the methods of the CI_Controller, which is a kind of "super class" that drives the whole framework.

Have a look at the loader class and the CodeIgniter class to grasp how CI internally works.

Agree with the answer above, but actually, load is a variable, not a function. it is a object of the class CI_Loader, when you call $this->load->libray(), in fact it calls the library() function in CI_Loader.

$this is nothing. It just use to store the value. It just like a variable.