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php

A reference problem

php.internals

Karoly Negyesi

20 years ago

Hi!

Without much ado, here is a piece of problematic code:

<?php
ini_set('error_report', E_ALL);
function f1() {
global $a;
$array = array();
$throwaway = f3($array);
var_dump($a);
}

function f2() {
global $a;
$array = array();
f3($array);
var_dump($a);
}

function f3($array) {
global $a;
$array[0] = &$a;
$array[0] = &$array[0]['foo']; // no notice here. interesting.
$array[0] = 'bar';
return $array;
}

$a = array();
f1();
$a = array();
f2();
?>

Please note that the only difference between f1 and f2 that the first
records the return value of f3() into a variable. However, this changes
the output:

array(1) {
["foo"]=>
&string(3) "bar"
}
array(1) {
["foo"]=>
string(3) "bar"
}

Is this a bug? Or I miss something?

Thanks

Karoly Negyesi

Ps. There is a good reason for using such ugly reference magic, and I am
happy to explain it to anyone who is interested, but it's a long story...

Etienne Kneuss

20 years ago

Hi,

Karoly Negyesi a écrit :

> > Please note that the only difference between f1 and f2 that the first
> > records the return value of f3() into a variable. However, this
> > changes the output:
> >
> > array(1) {
> >   ["foo"]=>
> >   &string(3) "bar"
> > }
> > array(1) {
> >   ["foo"]=>
> >   string(3) "bar"
> > }
> >
> > Is this a bug? Or I miss something?
>

When copying an array containing a reference, the reference is keeped. :

$value = 'foo';
$array = array (&$value);
$array2 = $array;
$array2[0] = 'bar';

echo $array[0]; // bar

Here, the &string(3) means that it's referenced. Indeed, $throwaway
contains a reference to it.

change your f1 to this :

function f1() {
global $a;
$array = array();
$throwaway = f3($array);
unset($throwaway);
var_dump($a);
}

And the "&" will obviously disappear, as the reference no longer exists.

Kind regards

-- Etienne Kneuss http://www.colder.ch/ colder@php.net

--
Etienne Kneuss

http://www.colder.ch/
colder@php.net