Accessing _POST and _GET dynamically using ${$varname}

Question

[FINAL EDIT]

Seems like I've been missing an important Warning contained in Variables variable PHP Manual http://www.php.net/manual/en/language.variables.variable.php :

Please note that variable variables cannot be used with PHP's Superglobal arrays within functions or class methods. The variable $this is also a special variable that cannot be referenced dynamically.

[ORIGINAL QUESTION]

I've encountered a problem trying to set/get html/server variables $_POST, $_GET, $_SESSION etc.. dynamically using a variable to hold it's name :

// Direct name
${'_GET'}['test'] = '1';

// Variable-holded name
$varname = '_GET';
${$varname}['test'] = '2';

echo "value is " . $_GET['test'];

will output :

value is 1

any idea why?

[EDIT 1] This is why I want to use it this way :

class Variable {
    protected static $source;

    public function __get($key) {

        // Some validation / var manip needed here

        if ( isset( ${self::$source}[$key] ) ) {
            return ${self::$source}[$key];
        }
    }

    public function __set($key, $value) {

        // Some validation / var manip needed here too
        ${self::$source}[$key] = $value;
    }
}

final class Get extends Variable {
    use Singleton;

    public static function create() {
        parent::$source = "_GET";
    }
}

final class Post extends Variable {
    use Singleton;

    public static function create() {
        parent::$source = "_POST";
    }
}

final class Session extends Variable {
    use Singleton;

    public static function create() {
        parent::$source = "_SESSION";
    }
}

create is called in the singleton constructor when instanciated

[EDIT 2] using PHP 5.4.3

Why to hell you want to set request variables' values???? They are not designed for that. :) — J0HN
– J0HN, Commented Feb 25, 2013 at 16:47
If you do not know whether to use GET or POST, you can use this: $var = empty($_POST) ? $_GET : $_POST; and then work with $var. — fedorqui
– fedorqui, Commented Feb 25, 2013 at 16:48
Aside from the dodgy getting of request variables, your code just ran completely fine for me :) — christopher
– christopher, Commented Feb 25, 2013 at 16:48
@fedorqui, and there's even a shorthand for that, called $_REQUEST. Well, it actually does more than just that... But 99.9% time you are not passing the same variable through both get, post and cookie, right? :) — J0HN
– J0HN, Commented Feb 25, 2013 at 16:51
Yes, right @J0HN! I discovered $_REQUEST some days ago and my brain still does not have it in cache : ) Thanks for highlighting it. — fedorqui
– fedorqui, Commented Feb 25, 2013 at 16:53

Sammitch · Accepted Answer · 2013-02-25 21:45:10Z

2

I'm guessing it has something to do with the fact that you shouldn't be assigning values to $_GET like that. Anyhow, this works just fine:

$source = '_GET';
echo ${$source}['test'];
// URL: http://domain.com/thing.php?test=yes
// output: "yes"

edit

Coincidentally, today I went back to update some old code where it looks like I was trying to implement exactly this inside of a class, and it wasn't working. I believe that using the global keyword before attempting to access a superglobal via a variable variable will solve your problem as well.

Class MyExample {
    private $method = '_POST';

    public function myFunction() {
        echo ${$this->method}['index']; //Undefined index warning
        global ${$this->method};
        echo ${$this->method}['index']; //Expected functionality
    }
}

edited Feb 25, 2013 at 21:45

answered Feb 25, 2013 at 17:00

Sammitch

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5 Comments

mcNdave Over a year ago

Yeah I got it to work, but I can't set vars this way. I was using it with _SESSION and it won't add/edit any values.

Sammitch Over a year ago

@user1990715 I can't think of a reason why it shouldn't work. If you can't get it working you might want to consider filing a bug about it.

mario Over a year ago

This only works in global scope IIRC. Referencing the superglobals per ${} local scope access is hindered by the way they're referenced in other contexts.

Sammitch Over a year ago

@mcNdave I've updated my answer with something that should solve your problem.

mcNdave Over a year ago

@Sammitch I've updated my original question with the answer, it simply is impossible. Your solution works fine with Get and Post, but when you're trying to set a Session variable, it won't update the session itself. Still, I may use it for my Get Post and Globals, thanks !

Hydra IO · Accepted Answer · 2013-02-25 16:47:03Z

1

You may be looking for variable variables. Taken from PHP.net:

<?php
$a = 'hello';
?>

<?php
$$a = 'world';
?>

<?php
echo "$a ${$a}";
//returns: hello world
//same as
echo "$a $hello";
?>

EDIT Another user on php.net had your exact question. Here is his answer.

<?php 
function GetInputString($name, $default_value = "", $format = "GPCS") 
    { 

        //order of retrieve default GPCS (get, post, cookie, session); 

        $format_defines = array ( 
        'G'=>'_GET', 
        'P'=>'_POST', 
        'C'=>'_COOKIE', 
        'S'=>'_SESSION', 
        'R'=>'_REQUEST', 
        'F'=>'_FILES', 
        ); 
        preg_match_all("/[G|P|C|S|R|F]/", $format, $matches); //splitting to globals order 
        foreach ($matches[0] as $k=>$glb) 
        { 
            if ( isset ($GLOBALS[$format_defines[$glb]][$name])) 
            {    
                return $GLOBALS[$format_defines[$glb]][$name]; 
            } 
        } 

        return $default_value; 
    } 
?>

answered Feb 25, 2013 at 16:47

Hydra IO

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1 Comment

J0HN Over a year ago

Am I the only person that feels that code (1) ugly, (2) won't work?

Mavelo · Accepted Answer · 2013-02-25 16:50:04Z

0

Why not just use $_REQUEST which includes $_GET, $_POST and $_COOKIE? Or am I misunderstanding the purpose?

answered Feb 25, 2013 at 16:50

Mavelo

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