global Overwrites¶

<?php

$argv = [1,2,3];
$_POST = [1,2,3];

function foo(?array $argv = null) {
    if ($argv === null) {
        global $argv;
    }

    print_r($argv);
}

foo();
foo([4,5,6]);

The global keyword is actually enough to overwrite a local variable.

In this illustration, the default value is used to trigger fetching the global variable $argv. The instruction is alone in the block, but it actually replaces the current variable, aka the parameter, by the global one. No assignation in sight, merely a surprise.

This won’t work with superglobal, such as $_POST, which can’t be overwritten by a parameter.

See Also¶

global Overwrites [Try me]

PHP Error Messages¶

Cannot re-assign auto-global variable %s

PHP Features¶

Last updated: 14 July 2026