- var_dump: documentation ( source)
- defined: documentation ( source)
- define: documentation ( source)
<?php
define("DEFINE",1);
define("HELLO", 'this_exists');
define("this_doesnt_exist", "HELLO");
$vvar = "this_doesnt_exist";
var_dump(
defined("DEFINE"), // true expected
defined(DEFINE), // false expected
defined("HELLO"), // true expected
defined(this_doesnt_exist), // true expected
defined($vvar) // true expected
);