How do I set an absolute include path in PHP?

One strategy

I don't know if this is the best way, but it has worked for me.

$root = $_SERVER['DOCUMENT_ROOT'];
include($root."/path/to/file.php");

The include_path setting works like $PATH in unix (there is a similar setting in Windows too).It contains multiple directory names, seperated by colons (:). When you include or require a file, these directories are searched in order, until a match is found or all directories are searched.

So, to make sure that your application always includes from your path if the file exists there, simply put your include dir first in the list of directories.

ini_set("include_path", "/your_include_path:".ini_get("include_path"));

This way, your include directory is searched first, and then the original search path (by default the current directory, and then PEAR). If you have no problem modifying include_path, then this is the solution for you.

What I do is put a config.php file in my root directory. This file is included by all PHP files in my project. In that config.php file, I then do the following;

define( 'ROOT_DIR', dirname(__FILE__) );

Then in all files, I know what the root of my project is and can do stuff like this

require_once( ROOT_DIR.'/include/functions.php' );

Sorry, no bonus points for getting outside of the public directory ;) This also has the unfortunate side affect that you still need a relative path for finding config.php, but it makes the rest of your includes much easier.