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Doc Bug #47400 Variable variables don't work with "global" inside a function
Submitted: 2009-02-16 04:20 UTC Modified: 2009-02-16 11:40 UTC
From: php at richardneill dot org Assigned:
Status: Not a bug Package: Documentation problem
PHP Version: Irrelevant OS:
Private report: No CVE-ID: None
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 [2009-02-16 04:20 UTC] php at richardneill dot org 
Description:
------------
Note sure whether this is an actual bug, or an omission from the documentation. Anyway, it doesn't seem to work when we use "global" to bring a variable into scope within a function, iff that variable name is itself a variable variable.

The example below is the shortest possible demonstration of the problem I can create (sorry it looks very contrived).

Thanks for your help.

Reproduce code:
---------------
<?
$fruit = "apple";
$lunch = "fruit";
$eat1 = $$lunch;
echo "Tasty: $eat1\n";   // apple, as expected

function nom ($meal) {   //$meal contains the string 'lunch'
  $eat2=$$meal;          //$eat2 should be the variable $lunch
  global $eat2;          //...which we bring into scope using "global"
  echo "Tasty: $eat2\n"; //Should give "apple", but doesn't.
}

nom ('lunch');
?>


Expected result:
----------------
Tasty: apple
Tasty: apple


Actual result:
--------------
Tasty: apple
Tasty:

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 [2009-02-16 04:24 UTC] preinheimer@php.net 
Does the third comment on this page address your concerns?

http://www.php.net/manual/en/language.variables.superglobals.php
 [2009-02-16 04:31 UTC] preinheimer@php.net 
also: http://www.php.net/manual/en/language.variables.variable.php

Where could we have put this information to make it easier for you to find? (so as to help other developers in the future)
 [2009-02-16 05:09 UTC] php at richardneill dot org 
Thanks for your response. 

The thing is, I'm NOT accessing $eat2 via the $GLOBALS superglobals array. All I'm doing is using the "global" keyword to bring it into scope in *this* specific function.

The note here:
http://uk2.php.net/manual/en/language.variables.variable.php
is indeed suggestive that there might be a problem (that's why I filed this as a probable documentation bug), but surely if it's $GLOBALS that can't be used with variable variables, it means that I just can't write:  $$GLOBALS["eat2"]       ?
 [2009-02-16 11:40 UTC] kalle@php.net 
Bogus, because your example is wrong:

function nom ($meal) {       // Say $meal = 'lunch'
  $eat2=$$meal;              // Here you get the value of the variable '$lunch' because $$meal = $lunch, and since $lunch isn't in this scope an E_NOTICE will be generated and $eat2 will be NULL
  global $eat2;              // Globalizing the variable $eat2 which doesn't exists
  echo "Tasty: $eat2\n";     // Output: Tasty: 
}
 
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