Declaring strings global?

[Gary_King]

What does global do? For example:

<?php
$a = 1;
$b = 2;

function Sum()
{
    global $a, $b;

$b = $a + $b;
} 

Sum();
echo $b;
?>

What would global do here? Please explain as simply as possible, because I didn't quite understand the explanation at PHP.net

[daynah]

Just follow through the script. 🙂

Well, we start out with, $a = 1, and $b = 2;

Then a function is defined.

Sum(); -- then the function is called.
$a then has the value of 1.
$b has the value of 3.

And then you print out the value of $b.

Because in the function the value of $a and $b are global, the value of the main $a and $b are changed.

So instead of the original values of:
$a = 1;
$b = 2;

It is now:
$a = 1;
$b = 3;

If the function was this (without the global vars):

<?php
$a = 1;
$b = 2;

function Sum()
{
    $b = $a + $b;
} 

Sum();
echo $b;
?>

The values of $a = 1 and $b =2.

The reason is that the function did NOT change the value of $b. It only changes a LOCAL copy of the variable inside the function Sum(), but not outside of it.

I hope this is understandable. If you have anymore questions, feel free to ask. 🙂

[Gary_King]

Thanks for the clarification 🙂

This is pretty much what I thought - global will set variables even after they have been processed by a function, correct?