Different behavior of PHP’s include/require on Windows and CentOS - php

Question

These are code of my PHP applications myApp.phpand mypartsA/main.php.
myApp.php
<?php
echo ("##### myApp is starting now !!! </br>");
require_once('/parts/mypartsA/main.php');
?>
mypartsA/main.php
<?php
echo ("#### mypartsA is required </br>");
?>
And myApp.php and mypartsA/main.php are in following structure.
Document_root
|
+--- test
| |
| +--- myApp.php
|
+--- parts
|
+--- mypartsA
|
+---main.php
I’ve used this application on Windows+Apache for a year with no problem but recently I migrate this to CentOS+Apache then I get fatal error related to include_path
PHP Warning: require_once(/parts/mypartsA/main.php)
[<a href='function.require-once'>function.require-once</a>]
: failed to open stream
: No such file or directory
in /var/www/html/test/myApp.php on line 12
PHP Fatal error: require_once() [<a href='function.require'>function.require</a>]
: Failed opening required (/parts/mypartsA/main.php’
(include_path='.:/php/includes:/usr/share/pear:/usr/share/pear/PEAR:/var/www/html')
in /var/www/html/test/myAPP.php on line 12
According to PHP.net if a path is defined the include_path will be ignored.
http://www.php.net/manual/en/function.include.php
I think in my case PHP tries to find parts directory from C:\ or / not from include_path.
require_once(/parts/mypartsA/main.php);
Therefore result of myAPP.php must be fatal error whether on Windows or on CentOS.
But my application has been working for a year with no error on Windows. PHP can find parts directory correctly.
Can sameone try those codes above on Windows and see..
##### myApp is starting now !!!
#### mypartsA is required
or get error?
Now,I want to know is why results of same code are different between running on Windows and running on CentOS.
What dirctive in PHP.ini do I have to check ?
I know if I change this code to add absolute path with $ _SERVER['DOCUMENT_ROOT'].
require_once($_SERVER['DOCUMENT_ROOT']./parts/mypartsA/main.php);
It’ll work well. But there are many applications with same style of coding and I don’t want to change all of them.
These are additional information.
include_path values phpinfo() shows on Windows
.;C:\PHP;C:\PHP\pear;C:\Apache2.2.22\htdocs
include_path values phpinfo() shows on CentOS
.:/php/includes:/usr/share/pear:/usr/share/pear/PEAR:/var/www/html

Answer 1

$path = realpath(dirname(__FILE__)) . "/../../parts/mypartsA/main.php";
require_once($path);
try with this path
$path = "../parts/mypartsA/main.php";
the second path should work with document root.