Access a global variable in a PHP function

Question

According to the most programming languages scope rules, I can access variables that are defined outside of functions inside them, but why doesn\'t this code work?

Answer 1

If you want, you can use the "define" function, but this function creates a constant which can't be changed once defined.

<?php
    define("GREETING", "Welcome to W3Schools.com!");

    function myTest() {
        echo GREETING;
    }

    myTest();
?>

PHP Constants

Answer 2

It's a matter of scope. In short, global variables should be avoided so:

You either need to pass it as a parameter:

$data = 'My data';

function menugen($data)
{
    echo $data;
}

Or have it in a class and access it

class MyClass
{
    private $data = "";

    function menugen()
    {
        echo this->data;
    }

}

See @MatteoTassinari answer as well, as you can mark it as global to access it, but global variables are generally not required, so it would be wise to re-think your coding.

Answer 3

For many years I have always used this format:

<?php
    $data = "Hello";

    function sayHello(){
        echo $GLOBALS["data"];
    }

    sayHello();
?>

I find it straightforward and easy to follow. The $GLOBALS is how PHP lets you reference a global variable. If you have used things like $_SERVER, $_POST, etc. then you have reference a global variable without knowing it.