当我手动为$ _POST数组赋值时，为什么filter_input（）返回NULL？

Question

I'm following some exercises about data validation and decided to mess around with the filter_input() function. When I try to run this code:

$_POST['var'] = 10;

$filtered = filter_input(INPUT_POST, 'var', FILTER_VALIDATE_FLOAT);

var_dump($filtered);

var_dump($filtered) returns NULL. I know the code works if $_POST['var'] is assigned a value by submitting a form, but I'm just wondering why manually assigning a value to the $_POST[] array doesn't return float(10)?

Answer 1

filter_input() doesn't read from the _POST/_GET/_COOKIE/_SERVER/_ENV superglobal arrays. It reads from the original sources of those values respectively (which are also used to populate the superglobals).