php - Global variables aren't working as expected with frameworks

Question

I'm trying to use global variables in my php script, and I found the usage of global variable on php.net. But it doesn't work on my local server. Is there any configuration I have missed out?

There is an example found on that page:

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

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

    $b = $a + $b;
} 

Sum();
echo $b;
?>

The above script will output 3.

However my output is 2!

Another example:

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

function Sum()
{
    $GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
} 

Sum();
echo $b;
?>

I get error:

Undefined index: a

So what is the deal with that? Why doesn't my code work as expected?
By they way, I'm using Laravel.

Answer 1

So as I guessed you are using a framework as you said in the comments:

@Rizier123 Yes, I'm using Laravel. Does it matter? – Kai 6 mins ago

And if it matters? Yes it does.

Probably what is happening here is, that the code which you show us here is wrapped into another function somewhere else.

Means that the variables in the Sum() function are in global scope, but the other ones outside of it not, since they are probably in another function == another scope.

---

You can reproduce it with this code:

function anotherFunction() {
    $a = 1;
    $b = 2;

    function Sum() {
        $GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
    } 

    Sum();
    echo $b;
}

anotherFunction();

And if you have error reporting on you will get:

Notice: Undefined index: a
Notice: Undefined index: b
2

Just put the error reporting at the top of your file(s) to get useful error messages:

<?php
    ini_set("display_errors", 1);
    error_reporting(E_ALL);
?>

To solve this now you have to declare the variables also in global scope, either with:

$GLOBALS["a"] = 1;
$GLOBALS["b"] = 2;

or like this:

global $a, $b;
$a = 1;
$b = 2;