CodeIgniter - best place to declare global variable

Question

I just want to use a $variable at several places: not only views and controllers, but also in the routes.php and other configuration files.

Answer 1

inside file application/conf/contants.php :

global $myVAR;
$myVAR= 'http://'.$_SERVER["HTTP_HOST"].'/';

and put in some header file or inside of any function:

global $myVAR;
$myVAR= 'some value';