global variables in php not working as expected

Question

I'm having trouble with global variables in php. I have a $screen var set in one file, which requires another file that calls an initSession() defined in yet another file. The initSession() declares global $screen and then processes $screen further down using the value set in the very first script.

How is this possible?

To make things more confusing, if you try to set $screen again then call the initSession(), it uses the value first used once again. The following code will describe the process. Could someone have a go at explaining this?

$screen = "list1.inc";            // From model.php
require "controller.php";         // From model.php
initSession();                    // From controller.php
global $screen;                   // From Include.Session.inc  
echo $screen; // prints "list1.inc" // From anywhere
$screen = "delete1.inc";          // From model2.php
require "controller2.php"         
initSession();
global $screen;
echo $screen; // prints "list1.inc" 

Update:
If I declare $screen global again just before requiring the second model, $screen is updated properly for the initSession() method. Strange.

Answer 1

If you have a lot of variables you want to access during a task which uses many functions, consider making a 'context' object to hold the stuff:

//We're doing "foo", and we need importantString and relevantObject to do it
$fooContext = new StdClass(); //StdClass is an empty class
$fooContext->importantString = "a very important string";
$fooContext->relevantObject = new RelevantObject();

doFoo($fooContext);

Now just pass this object as a parameter to all the functions. You won't need global variables, and your function signatures stay clean. It's also easy to later replace the empty StdClass with a class that actually has relevant methods in it.