include - PHP: A working file doesn't find other files after inclusion? -

first of all: sorry title. if can make replace it, please since didn't know how name problem in first place. said, there possibly duplicates around, figured need on thing , didn't know search for...

the base site wasn't made me. written in html, inclusions done php , don't way made. getting irrelevant question i'm trying ask here.

the files described here contain more stuff what's written here, problem here that
when requiring file requires file b requires many files, file b can't find files it's looking for.

so let's got directory tree like:

| - project +--- lower.txt | -- stuff | ---- case +------ index.php +------ upper.php | -- gallery +---- main.php +---- config.php +---- miscfunc.php +---- css.php 

project\stuff\case\index.php:

<?php include("./upper.php");?> ... <?php include("../../lower.txt");?> 

project\stuff\case\upper.php:

<?php require_once("../../gallery/main.php"); ?> 

project\gallery\main.php:

<?php namespace gallery; ... // i'm trying debug here... : // -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- //  $pathtoscan = "./"; // scan current directory, point /project/stuff/case/  function scanfolder($path) {     $array = array();     if ($dir = @opendir($path)) {         while (($file = readdir($dir)) !== false) {             $array[] = $file;         }         printf("current directory: %s<br/>\n", dirname(__file__));         printf("document_root: %s<br/>\n", $_server["document_root"]);         printf("scan directory: %s<br/>\n<br/>\n", $path);         var_dump($array);     } } scanfolder($pathtoscan);  // -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- //  require_once("./config.php"); // these files in gallery namespace require_once("./miscfunc.php"); require_once("./css.php"); ...  ... ?> 

so... when execute project\stuff\case\index.php get:

current directory: c:\xampp\htdocs\project\gallery document_root: c:/xampp/htdocs scan directory: ./  array(4) { [0]=> string(1) "." [1]=> string(2) ".." [2]=> string(9) "index.php" [3]=> string(7) "upper.php" } warning: require_once(./config.php) [function.require-once]: failed open stream: no such file or directory in c:\xampp\htdocs\project\gallery\main.php on line 44  fatal error: require_once() [function.require]: failed opening required './config.php' (include_path='.;c:\xampp\php\pear') in c:\xampp\htdocs\project\gallery\main.php on line 44 

now why happen, , how can working without moving files , preferably without breaking main.php?

i ended changing

require_once("./filename.php"); 

rows to

require_once(__dir__ . "/filename.php"); 

still wondering if have been done otherwise...