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Variable Variables and Superglobals

php.internals

A.Rico

22 years ago

Using Variable Variables works fine inside functions for global
defined variables if you declare them as global inside the function.
Suprinsingly, it does not seem to work with superglobals. Take the
following example:

// code ////////////////////////////////////////////////////////////

<?php
$glob_var="Var 1";

$var_glob_var="glob_var";
$var_ENV="_ENV";

echo $_ENV["OS"],"\n";
echo $glob_var,"\n\n";

echo $var_glob_var,"\n";
echo $var_ENV,"\n\n";

echo $$var_glob_var,"\n";
echo ${$var_ENV}["OS"],"\n\n";

foo1($var_glob_var);
foo2($var_glob_var);
foo3();
foo4();
foo5($var_ENV);
foo6($var_ENV);
foo7();
foo8();
foo9();

function foo1($arg){
echo "--- In foo1 --------------\n";
echo $arg,"\n";
echo $$arg,"\n";
echo "--------------------------\n";
}
function foo2($arg){
global $glob_var;

echo "--- In foo2 --------------\n";
echo $arg,"\n";
echo $$arg,"\n";
echo "--------------------------\n";
}
function foo3(){
$arg="glob_var";
echo "--- In foo3 --------------\n";
echo $arg,"\n";
echo $$arg,"\n";
echo "--------------------------\n";
}
function foo4(){
global $glob_var;

$arg="glob_var";
echo "--- In foo4 --------------\n";
echo $arg,"\n";
echo $$arg,"\n";
echo "--------------------------\n";
}
function foo5($arg){
echo "--- In foo5 --------------\n";
echo $arg,"\n";
echo ${$arg}["OS"],"\n";
echo "--------------------------\n";
}
function foo6($arg){
global $_ENV;

echo "--- In foo6 --------------\n";
echo $arg,"\n";
echo ${$arg}["OS"],"\n";
echo "--------------------------\n";
}
function foo7(){
$arg="_ENV";

echo "--- In foo7 --------------\n";
echo $arg,"\n";
echo ${$arg}["OS"],"\n";
echo "--------------------------\n";
}
function foo8(){
global $_ENV;
$arg="_ENV";

echo "--- In foo8 --------------\n";
echo $arg,"\n";
echo ${$arg}["OS"],"\n";
echo "--------------------------\n";
}
function foo9(){
echo "--- In foo9 --------------\n";
echo $_ENV["OS"],"\n";
echo "--------------------------\n";
}
?>

// Output /////////////////////////////////////////////////////////

Windows_NT
Var 1

glob_var
_ENV

Var 1
Windows_NT

--- In foo1 --------------
glob_var

--------------------------
--- In foo2 --------------
glob_var
Var 1
--------------------------
--- In foo3 --------------
glob_var

--------------------------
--- In foo4 --------------
glob_var
Var 1
--------------------------
--- In foo5 --------------
_ENV

--------------------------
--- In foo6 --------------
_ENV

--------------------------
--- In foo7 --------------
_ENV

--------------------------
--- In foo8 --------------
_ENV

--------------------------
--- In foo9 --------------
Windows_NT
--------------------------

// Version //////////////////////////////////////////////

PHP 4.3.7 (cgi-fcgi) (built: Jun  2 2004 15:49:31)
Copyright (c) 1997-2004 The PHP Group
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies

// End //////////////////////////////////////////////////

I'm doing something wrong? Or this is the expected behavior?

Thank you in advance

Andi Gutmans

22 years ago

Right. Variable variables don't work with super-globals and I think it is
documented in this way.
This is on purpose as we decided to only support them this way both for
clarity reasons and for performance.
There are no plans to change this.

Andi

At 01:35 AM 8/5/2004 +0200, A.Rico wrote:

A.Rico

22 years ago

What the PHP documentation says about variable variables and
superglobals is that you can't use them as a "pointer":

/*Warning*/

/ Please note that variable variables cannot be used with PHP's
Superglobal arrays
<http://www.php.net/manual/en/language.variables.predefined.php#language.variables.superglobals>.
This means you cannot do things like ${$_GET}. If you are looking
for a way to handle availability of superglobals and the old
HTTP_*_VARS, you might want to try referencing
<http://www.php.net/manual/en/language.references.php> them. /

what I intended was to use a "normal" globally defined variable to
"point" to a superglobal; that, in fact, works in the global scope, but
not in the function scope:

// Code //////////////////////////////////////////////////////////////
$varvar="_ENV";

echo $_ENV["OS"]; // --> Windows NT
echo ${$varvar}; // --> Windows NT

foo($varvar);

function foo($arg){
$lvar="_ENV";

echo $_ENV["OS"]; // --> Windows NT
echo ${$arg}["OS"]; // --> *nothing*
echo ${$lvar}["OS"]; // --> *nothing*
var_dump( $$arg ); // --> NULL
var_dump( $$lvar); // --> NULL
}
// END //////////////////////////////////////////////////////////////

Regards,

A. Rico

Curt Zirzow

22 years ago

* Thus wrote A.Rico:

>    What the PHP documentation says about variable variables and
> superglobals is that you can't use them as a "pointer":
>
>    /*Warning*/
>
>    / Please note that variable variables cannot be used with PHP's
>    Superglobal arrays
>    <http://www.php.net/manual/en/language.variables.predefined.php#language.variables.superglobals>.
>    This means you cannot do things like ${$_GET}. If you are looking
>    for a way to handle availability of superglobals and the old
>    HTTP_*_VARS, you might want to try referencing
>    <http://www.php.net/manual/en/language.references.php> them. /
>
> what I intended was to use a "normal" globally defined variable to
> "point" to a superglobal; that, in fact, works in the global scope, but
> not in the function scope:
>
> // Code //////////////////////////////////////////////////////////////
> $varvar="_ENV";
>
> echo $_ENV["OS"]; // --> Windows NT
> echo ${$varvar}; // --> Windows NT

This is a documentation issue, i believe, as noted on:
http://php.net/variables.predefined

Variable variables super globals aren't allowed inside functions or
methods. The waring on the page you reference is fixed in the docs
reflecting this.

Curt

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Sara Golemon

22 years ago

> function foo($arg){
>     $lvar="_ENV";
>
>     echo $_ENV["OS"]; // --> Windows NT
>     echo ${$arg}["OS"]; // --> *nothing*
>     echo ${$lvar}["OS"]; // --> *nothing*
>     var_dump( $$arg ); // --> NULL
>     var_dump( $$lvar); // --> NULL
> }
> // END //////////////////////////////////////////////////////////////
>

echo $GLOBALS[$lvar]['OS'];