I know this error is dicussed often already, but I just can't use require or include in my function.php(xampp) without this error on the top and I don't have a php.ini file. I don't even want one, if not necessary!
I just want to include a second php file in the fuction.php. Come on that can't be so hard...
That's what I used.
require_once (get_stylesheet_directory_uri().'/index.php');
(result: http://localhost/werkstatt/wp-content/themes/twentysixteen/index.php)
I mean in this case the index.php would be inluded anyway which leads me to the second question. Why or how are some standard files like index.php already inluded?