Syntax in function does not work

I dont understand exactly what you try to do. You have to go with the MVC pattern with CI. So all of your database stuff should organized in a model like

PHP Code:

class Example_model extends CI_Model {
    function __construct()
    {
    }

    public function get($table, $id = false)
    {
        if ($id)
        {
            $this->db->where('id', $id);
        }
        $query = $this->db->get($table);
        if($query->num_rows() > 0)
        {
            return $query->result_array();
        }
        return false;
    }

    // etc.
} 


Then in all of your controller files you can call your model methods like that

PHP Code:

class Example extends CI_Controller {

    public function __construct()
    {
        parent::__construct();
        $this->load->model('example_model');
    }

    public function index()
    {
       $this->example_model->get('users');
    }
}