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

Global DOES NOT make the variable global. I know it’s tricky 🙂

Global says that a local variable will be used as if it was a variable with a higher scope.

E.G :

<?php  $var = 'test'; // this is accessible in all the rest of the code, even an included one  function foo2() {     global $var;     echo $var; // this print 'test'     $var = 'test2'; }  global $var; // this is totally useless, unless this file is included inside a class or function  function foo() {     echo $var; // this print nothing, you are using a local var     $var = 'test3'; }  foo(); foo2(); echo $var;  // this will print 'test2' ?> 

Note that global vars are rarely a good idea. You can code 99.99999% of the time without them and your code is much easier to maintain if you don’t have fuzzy scopes. Avoid global if you can.