how to display username in header using session

You get 1 because you are setting the user_id with the value of $login_id and not the username with the value of $username

PHP Code:

$this->session->set_userdata('user_id',$login_id); 


So also set the username

PHP Code:

$this->session->set_userdata('username',$username); 


And what type of value is returned for $login_id?