Change working directory

Question

Sorry for asking again, but I really need help. I have header.php in the root/lib which is including header_sub.php in the same directory. Normally files in root can directly include them by this code:

include_once('lib/header.php');

but now i have example.php in a sub-directory /blog, if i use these

include_once(../'lib/header.php');  or 
include_once($_SERVER['DOCUMENT_ROOT'].'/lib/header.php');  or 
include_once(dirname(__FILE__).'/lib/header.php');

header_sub.php would not be included correctly.

Is there a way to include header.php and header_sub.php without modifying them?

Some body suggested to use these:

$oldcwd = getcwd(); // Save the old working directory
    chdir("../"); // Moves up a folder, so from /blog to /
    include("header.php"); // Include the file with the working directory as if the header file were being loaded directly, from it's folder
    chdir($oldcwd); // Set the working directory back to before

However, even i can see the current url is root directory after chdir(), it still includes this root/blog/lib......

Answer 1

The path to the file you need depends on were you are calling the file. Examples:

In /root calling file in /root -> include_once('header.php');
In /root calling file in /root/lib -> include_once('lib/header.php');
In /root/lib calling file in /root -> include_once('../header.php');
In /root/blog calling file in /root/lib -> include_once(../lib/'header.php');
In /root/blog/css calling file in /root/lib -> include_once(../../lib/'header.php');

If you do like this all path are relative and you can change the root folder and everything still works.

Another option is you have a file called "common.php" or "include.php" were you define path for some folders. This is useful if your site directory has many sub folders.