how to require_once in codeigniter
Use CodeIgniter's built in constant, APPPATH
require_once(APPPATH.'libraries/ion_auth.php');
If the library is a codeigniter specific library, as sbaaaang points out, you should use:
$this->load->library('ion_auth');However, if the library is just a generic PHP class or set of functions, the codeiginter loader may not recognize it. Then you will need to use either one of the generic loading operators (include, include_once, require, require_once), with the APPPATH constant, as also pointed out:
require_once(APPPATH.'libraries/ion_auth.php');
In a real server, you should use library's UPPERCASE name. like this:
require_once(APPPATH.'libraries/Ion_auth.php');