定义的变量未定义？

Question

Here is a shortened version of my code:

<?php
    $foo = "Bar";

    function test () {
        echo $foo; // Undefined variable?
    }

    test();
?>

I don't understand, why PHP says, that $foo is undefined. And I always find solutions for deactivating the error reporting, but I want to fix my code. What am I missing?

Answer 1

In PHP you cannot access global variables from functions unless you explicitly import them using global $foo;.

$foo = "Bar";
function test() {
    global $foo;
    echo $foo;
}
test();

Another option would be accessing it as $GLOBALS['foo'] - $GLOBALS is a special array that "contains" the global scope and is available wverywhere.

However, using global variables is usually a bad idea that results in spaghetti code. Try to avoid them. Usually the correct way is to make the variable a function argument:

function test($foo) {
    echo $foo;
}
test('bar');