Question

If I have an index.php file that includes inc/footer.php I would write:

include 'inc/footer.php';

If I want to include another file inside footer.php, I must do it relative to the index.php file (the one that is including it). This may not be a problem, but what about if I want to include index.php from an entire different location?

I understand that there are several methods to achieve this like defining an absolute path or using dirname(__FILE__).

This is something that has never been a real problem since one way or another I always figured it out but that I always wondered how exactly includes work in php.

Can someone explain me exaclty what is going on under the hood?

Answer 1

This may help: (from http://php.net/manual/en/function.include.php)

Files for including are first looked
for in each include_path entry
relative to the current working
directory, and then in the directory
of current script. E.g. if your
include_path is libraries, current
working directory is /www/, you
included include/a.php and there is
include "b.php" in that file, b.php
is first looked in /www/libraries/
and then in /www/include/. If filename
begins with ./ or ../, it is looked
for only in the current working
directory or parent of the current
working directory, respectively

Your question states:

If I want to include another file
inside footer.php, I must do it
relative to the index.php file (the
one that is including it).

This is true only if the filepath you are trying to include() starts with ./ or ../ . If you need to include a file above the current file using a relative path, you can (as you suggested) use:

include dirname(__FILE__) . '/../file.php';

---

If you define an absolute path, you can also add this to the current include_path:

set_include_path(get_include_path() . PATH_SEPARATOR . '/absolute/path');

You can then do all your includes relative to ‘/absolute/path/’.