RE: [PHP] Possible foreach bug; seeking advice to isolate the problem
-Original Message-
From: Jonathan Sachs [mailto:081...@jhsachs.com]
Sent: 20 October 2010 04:48
To: php-general@lists.php.net
Subject: [PHP] Possible foreach bug; seeking advice to isolate the
problem
I've got a script which originally contained the following piece of
code:
foreach ( $objs as $obj ) {
do_some_stuff($obj);
}
When I tested it, I found that on every iteration of the loop the
last
element of $objs was assigned the value of the current element. I
was
able to step through the loop and watch this happening, element by
element.
All the other suggestions I've seen on this are essentially correct -- before
the foreach runs, something somewhere has set $obj to be a reference to the
last element of the array.
It really doesn't matter whether you can find the culprit for this or not --
the solution is simply to put an
unset($obj)
immediately before the foreach statement -- this will break the reference
(without destroying anything but $obj!) and make the foreach behave exactly as
you want.
Cheers!
Mike
--
Mike Ford,
Electronic Information Developer, Libraries and Learning Innovation,
Leeds Metropolitan University, C507 City Campus,
Woodhouse Lane, LEEDS, LS1 3HE, United Kingdom
Email: m.f...@leedsmet.ac.uk
Tel: +44 113 812 4730
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Re: [PHP] Possible foreach bug; seeking advice to isolate the problem
On 20/10/2010 05:47, Jonathan Sachs wrote:
I've got a script which originally contained the following piece of
code:
foreach ( $objs as $obj ) {
do_some_stuff($obj);
}
When I tested it, I found that on every iteration of the loop the last
element of $objs was assigned the value of the current element. I was
able to step through the loop and watch this happening, element by
element.
Are you are using a 'referencing' foreach? i.e.
foreach ($objs as $obj) {
do_some_stuff($obj);
}
or is the above code a direct lift from your script?
Referencing foreach statements can cause problems as the reference to
the last array entry is persistent after the foreach loop has terminated
so any further foreach statements on the same array will overwrite the
previous reference which is still pointing to the last item.
Rich
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[PHP] Possible foreach bug; seeking advice to isolate the problem
I've got a script which originally contained the following piece of
code:
foreach ( $objs as $obj ) {
do_some_stuff($obj);
}
When I tested it, I found that on every iteration of the loop the last
element of $objs was assigned the value of the current element. I was
able to step through the loop and watch this happening, element by
element.
I originally encountered this problem using PHP v5.2.4 under Windows
XP. I later reproduced it in v5.3.2 under XP.
The function call wasn't doing it. I replaced the function call with
an echo statement and got the same result.
For my immediate needs, I evaded the problem by changing the foreach
loop to a for loop that references elements of $objs by subscript.
That leaves me with the question: what is going wrong with foreach?
I'm trying to either demonstrate that it's my error, not the PHP
engine's, or isolate the problem in a small script that I can submit
with a bug report. The current script isn't suitable for that because
it builds $objs by reading a database table and doing some rather
elaborate manipulations of the data.
I tried to eliminate the database by doing a var_export of the array
after I built it, then assigning the exported expression to a variable
immediately before the foreach. That broke the bug -- the loop
behaved correctly.
There's a report of a bug that looks similar in the comments section
of php.net's manual page for foreach, time stamped 09-Jul-2009 11:50.
As far as I can tell it was never submitted as a bug and was never
resolved. I sent an inquiry to the author but he didn't respond.
Can anyone make suggestions on this -- either insights into what's
wrong, or suggestions for producing a portable, reproducible example?
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