PHP :: Doc Bug #20993 :: Element value changes without asking

Doc Bug #20993

Element value changes without asking

Submitted:

2002年12月13日 12:00 UTC

Modified:

2004年07月26日 17:16 UTC

Votes:	5
Avg. Score:	4.4 ± 0.8
Reproduced:	3 of 3 (100.0%)
Same Version:	0 (0.0%)
Same OS:	1 (33.3%)

From:

henrik dot gebauer at web dot de

Assigned:

Status:

Closed

Package:

Documentation problem

PHP Version:

4.0CVS-2002年12月13日

OS:

Any

Private report:

CVE-ID:

None

View Developer Edit

[2002年12月13日 12:00 UTC] henrik dot gebauer at web dot de

I create an array an then a reference to an element of that array.
Then the array is passed to a function (by value!) which changes the value of the element.
After that, the global array has also another value.
I would expect this behaviour if I passed the array by reference but I did not.
<?php
$array = array(1);
$reference =& $array[0];
echo $array[0], '<br>';
theFunction($array);
echo $array[0], '<br>';
function theFunction($array) {
 $array[0] = 2;
}
?>

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[2002年12月13日 12:42 UTC] msopacua@php.net

Verified and added testcase to CVS

[2002年12月13日 12:50 UTC] moriyoshi@php.net

Verified with 4.2.3

[2002年12月13日 14:51 UTC] moriyoshi@php.net

This bug has a lot to do with the bug reports mentioned below.
http://bugs.php.net/bug.php?id=6417
http://bugs.php.net/bug.php?id=7412
http://bugs.php.net/bug.php?id=15025
As a workaround, you can write as following to avoid this issue.
function theFunction($array) {
 $array = unserialize(serialize($array));
 
 $array[0] = 2;
}

[2002年12月18日 03:25 UTC] msopacua@php.net

We have discussed this issue and it will put a considerable slowdown on php's performance, to fix this properly.
Therefore this behavior will be documented.

[2004年04月16日 22:59 UTC] php dot devel at homelinkcs dot com

I don't wish to generate unnecessary traffic, however, I 
have been unable to find any reference to this issue in 
the current documentation at http://www.php.net/manual. 
Since, it's been well over a year since this issue (and 
several related bug reports) has been brought up, can 
anyone give me an update on this it's status? I consider 
this a serious problem because, IMHO, the behavior seems 
illogical from a high-level view of references and copies 
(cf (from chapter 7 of the manual): "[A]fter assigning one 
variable's value to another, changing one of those 
variables will have no effect on the other."). For that 
reason, furthermore, lack of knowedge of this behavior 
can make code affected by it quite difficult to debug.

[2004年04月17日 17:59 UTC] nlopess@php.net

As you may have noted, we have more than 100 open bugs, so its hard to response quickly.
However, if you want to submit a patch to the documentation, we are open to contributions.

[2004年04月22日 01:34 UTC] php dot devel at homelinkcs dot com

This is my best effort (with the help of a friend), to 
document this issue. I have based it on my personal tests 
as well as information from this and related bug reports, 
but I assume it goes without saying that this patch should 
be reviewed by a developer with knowledge in this area 
before being committed. Thanks for a great programing 
language! 
 
 
Index: references.xml 
=================================================================== 
RCS file: /repository/phpdoc/en/language/references.xml,v 
retrieving revision 1.27 
diff -u -r1.27 references.xml 
--- references.xml	2003年12月21日 15:37:29	1.27 
+++ references.xml 2004年04月21日 19:20:39 
@@ -43,6 +43,21 @@ 
 </para> 
 </note> 
 </para> 
+ <warning> 
+ <simpara> 
+ Due to peculiarities of the internal workings of 
PHP, if a reference 
+ is made to a single element of an array and then the 
array is copied, 
+ whether by assignment or when passed by value in a 
function call, 
+ the reference is copied as part of the array. This 
means that 
+ changes to any such elements in either array will be 
duplicated in 
+ the other array (and in the other references), even 
if the arrays 
+ have different scopes (e.g. one is an argument 
inside a function and 
+ the other is global)! Elements that did not have 
references at the 
+ time of the copy, as well as references assigned to 
those other 
+ elements after the copy of the array, will behave 
normally (i.e. 
+ independent of the other array). 
+ </simpara> 
+ </warning> 
 <para> 
 The same syntax can be used with functions, that 
return references, 
 and with <literal>new</literal> operator (in PHP 4.0.4 
and later):

[2004年04月25日 20:32 UTC] nlopess@php.net

Looks good. any objection?

[2004年05月03日 23:46 UTC] php dot devel at homelinkcs dot com

I don't have any objection. :-D

[2004年07月26日 17:16 UTC] vrana@php.net

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.
Thank you for the report, and for helping us make our documentation better.