Overriding scope with the GLOBALS array - Practical PHP Programming

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At some point in your PHP programming career you will want to read a global variable inside a function - I can pretty much guarantee that, because it is a very popular thing to do. Luckily, it is made easy for you by PHP through the $GLOBALS superglobal array, which allows you to access global variables even from within functions. When it comes to the $GLOBALS array it is quite simple: all variables declared in the global scope are in the $GLOBALS array, which you can access anywhere in the script.

To demonstrate this in action, consider the following script:

<?php

      function foo() {

          $GLOBALS['bar'] = "wombat";

      }

  

      $bar = "baz";

      foo();

      print $bar;
 ?>

What do you think that will output this time? If you guessed "wombat", you would be correct - the foo() function literally alters a variable outside of its scope, so that even after it returns control back to the main script, its effect is still felt. You can of course read variables in the same way, like this:

$localbar = $GLOBALS['bar'];

However, that is quite hard on the eyes. PHP allows you to use a special keyword, GLOBAL, to allow a variable to be accessed locally. For example:

function myfunc() {

      GLOBAL $foo, $bar, $baz;

      ++$baz;

  }

That would allow a function to read the global variables $foo, $bar, and $baz. The ++$baz line will increment $baz by 1, and this will be reflected in the global scope also.

DoctoR JackaL - 13 Oct 2008

Also want to note that when defining a variable using GLOBAL , the varaible names are written infront of GLOBAL , while the values on a new line for each varaible , example :

<?php
GLOBAL $A, $B, $C;
$A = "This is variable A";
$B = "This is variable B";
$C = "This is variable C";
?>

DoctoR JackaL - 13 Oct 2008

I'm using PHP 5.05 and found many thingZ not said here .

1) using $GLOBALS inside or outside a function will make the variable a GLOBAL variable and can only be used outside the function in the script itself .

2) using GLOBAL inside a function makes the variable use-able inside and outside functions.

3) using GLOBAL outside functions makes the variable GLOBAL and can only be used outside the functions.

The important note is number 2 , try it urself and c , this iz what i always get

chima/chytons@yahoo.com - 13 Oct 2008

Note that when using the GLOBAL keyword to access a global variable from within a function, it's an error to simutaneously declare the variable GLOBAL and assign it a value as in:

function myFunc() {
GLOBAL $foo = somevalue;
}

The declaration and assigment should be done separately as in:

function myFunc() {
GLOBAL $foo;
$foo = somevalue;
}

fredrik at demomusic dot nu - 13 Oct 2008

Just a reminder that passing by reference and/or using the $GLOBALS array gives you more control of the scope as opposed to using the GLOBAL-command.

Also, a reminder of that constants are global in nature is approriate.

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4.17 Overriding scope with the GLOBALS array

This is NOT the latest copy of this book; click here for the latest version.