How do you know the correct path to use in a PHP require_once() statement

Question

As many do I have a config.php file in the root of a web app that I want to include in almost every other php file. So most of them have a line like:

require_on         


        

Answer 1

The only place I've seen the path evaluated from is the file that you are currently editing. I've never had any problems with it, but if you are, you might want to provide more information (PHP version, OS, etc).