How to include WordPress functions in custom .php file?

Well if someone has newer PHP versions installed (ver >= 5.5.x) then they can also try the below code in the root script in WordPress website directory itself:

<?php
define("WP_ROOT", __DIR__);
define("DS", DIRECTORY_SEPARATOR);
require_once WP_ROOT . DS . "wp-load.php";

Or

<?php
define("WP_ROOT", __DIR__);
define("DS", DIRECTORY_SEPARATOR);
require_once WP_ROOT . DS . "wp-blog-header.php";

I guess this is a more direct and clean approach and doesn't involve manually adding slashes and changing diretories by ...

Hope this helps someone.

To use wp functions in custom .php files, you must include wp-load.php in your file. You can do so by adding the following line:

require_once(PATH_TO.'/wp-load.php');

If WordPress is in the document root add instead:

require_once($_SERVER['DOCUMENT_ROOT'].'/wp-load.php');

You're on the right track. Try this instead:

require_once("../../../../wp-load.php");