How to get the defined() value by a string?

Question

define('key_start_atz', 200);

$str = 'key_start_atz';

How can I get 200 via $str?

Answer 1

constant($str);

Answer 2

define('key_start_atz', 200);

$x = 'key_start_atz'; // contains 'key_start_atz'
$x = key_start_atz; // contains 200
$x = constant('key_start_atz'); // contains 200