PHP - Relative paths "require"

If you are including this files db.php and functions.php in index.php then you have to write this code

require "../db.php";
require "../functions.php";

OR if you are including this files in blog.php then write this code

require "db.php";
require "functions.php";

If you find that relative include paths aren't working as expected, a quick fix is to prepend __DIR__ to the front of the path you're trying to include.

require __DIR__ . "/../blog.php";

It's reasonably clean, and you don't need to modify the include path or working directory.

You need to set the include_path in your php.ini.

If you want to set it at run-time, use set_include_path().