php - calling include from an included file

Question

So, examining this directory structure

• /include_one.php
• /include_two.php
• /directory/main_file.php

Assume that I am in /directory/main_file.php and I call include('../include_one.php'); inside of include_one.php, to include include_two.php. Do I need to call include('include_two.php); or include('../include_two.php');?

So my question is: When including a file, is the 'relative include path' shifted to the included file, or does it remain at the main including file?

I am aware that the best alternative would be to have a config.php which contains the root_path, however this is not possible at this stage.

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update:
So, im not sure who is right, as here is my test

directory structure

/include.php
/start/start.php
/folder1/includeone.php
/folder1/folder2/includetwo.php

and here is the contents of each file

start.php

<?php 
  echo 'including ../include.php<br />';
  include('../include.php');
?>

include.php

<?php 
  echo 'including folder1/includeone.php<br />';
  include('folder1/includeone.php');
?>

includeone.php

<?php 
  echo 'including folder2/includetwo.php<br />';
  include('folder2/includetwo.php');
?>

includetwo.php

<?php 
  echo 'done<br />';
?>

and the output is

including ../include.php
including folder1/includeone.php
including folder2/includetwo.php
done

Answer 1

The "relative include path" is not shifted to the included file... Which means that using relative paths generally ends badly.

A better solution, that I use almost all the time, is to always work with absolute paths -- and you can mix relatives and absolute paths using __DIR__, to get the directory that contains the file where this is written.

For example, in include_one.php, you'd use :

require_once __DIR__ . '/include_two.php';

To include the include_two.php file that's in the same directory as include_one.php.

And, in main_file.php, you'd use :

require_once __DIR__ . '/../include_one.php';

To include the include_one.php file that's one directory up.

With that, your includes will work, no matter from which file they are called.