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Request #60944 Unable to detect if variable exists vs. is null
Submitted: 2012-02-01 08:05 UTC Modified: 2012-02-03 09:00 UTC
From: lampacz+php at gmail dot com Assigned:
Status: Wont fix Package: Variables related
PHP Version: 5.3.9 OS: Linux
Private report: No CVE-ID: None
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 [2012-02-01 08:05 UTC] lampacz+php at gmail dot com 
Description:
------------
There is no difference between $x = NULL and unset($a). So i'm unable to detect if variable was defined (so it can be defined and be filled with null)

http://www.php.net/manual/en/types.comparisons.php Table Comparisons of $x with PHP functions, rows 2 - 4 gives same results


Expected result:
----------------
Different results for undefined variables and null variables

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 [2012-02-01 09:54 UTC] laruence@php.net 
<?php
$a = null;
var_dump(array_key_exists('a', get_defined_vars())); //or $GLOBALS
?>
 [2012-02-01 10:39 UTC] lampacz+php at gmail dot com 
Marvelous.

Sugestion for new function: is_defined(mixed $var)

which internally return array_key_exists($var, get_defined_vars()); ?

Thank you for.
 [2012-02-02 02:00 UTC] phpmpan at mpan dot pl 
What is the rationale for introducing such function? Can you provide any real-life example when it is neccessary to distinguish between an undefined global variable and a global variable set to `NULL`? The question is important, as use of global variables is getting less popular. Adding a new function, that will duplicate already existing functionality (proposed by Laruence), is IMHO not a good idea.
 [2012-02-03 09:00 UTC] laruence@php.net
-Status: Open +Status: Wont fix
 [2012-02-03 09:00 UTC] laruence@php.net 
php is a loose-type language. there is no different between a null and a 
`undefined variable` . 

as I said above, you can use isset($GLOBALS[***]) to achieve your requirement.
 
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