safe to delete elements of array in foreach

[Jon Slaughter]

Is it safe to remove elements from an array that foreach is working on?
(normally this is not the case but not sure in php) If so is there an
efficient way to handle it? (I could add the indexes to a temp array and
delete afterwards if necessary but since I'm actually working in a nested
situation this could get a little messy. I guess I could set there values to
null and remove them afterwards?

Thanks,
Jon

[ZeldorBlat]

Re: safe to delete elements of array in foreach

On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
wrote:

Is it safe to remove elements from an array that foreach is working on?
(normally this is not the case but not sure in php) If so is there an
efficient way to handle it? (I could add the indexes to a temp array and
delete afterwards if necessary but since I'm actually working in a nested
situation this could get a little messy. I guess I could set there values to
null and remove them afterwards?
>
Thanks,
Jon

Why don't you try it and see what happens?

[Jon Slaughter]

Re: safe to delete elements of array in foreach


"ZeldorBlat " <zeldorblat@gma il.comwrote in message
news:1179501018 .125313.63600@p 77g2000hsh.goog legroups.com...

On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
wrote:

>Is it safe to remove elements from an array that foreach is working on?
>(normally this is not the case but not sure in php) If so is there an
>efficient way to handle it? (I could add the indexes to a temp array and
>delete afterwards if necessary but since I'm actually working in a nested
>situation this could get a little messy. I guess I could set there values
>to
>null and remove them afterwards?
>>
>Thanks,
>Jon

>
Why don't you try it and see what happens?
>

Um... cause I did... but that doesn't mean much. Just cause someone tries
something doesn't prove that it will always work like that...

got any more bright ideas?

Or is the question to hard for you?

[ZeldorBlat]

Re: safe to delete elements of array in foreach

On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
wrote:

"ZeldorBlat " <zeldorb...@gma il.comwrote in message
>
news:1179501018 .125313.63600@p 77g2000hsh.goog legroups.com...
>

On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
wrote:

Is it safe to remove elements from an array that foreach is working on?
(normally this is not the case but not sure in php) If so is there an
efficient way to handle it? (I could add the indexes to a temp array and
delete afterwards if necessary but since I'm actually working in a nested
situation this could get a little messy. I guess I could set there values
to
null and remove them afterwards?

>

Thanks,
Jon

>

Why don't you try it and see what happens?

>
Um... cause I did... but that doesn't mean much. Just cause someone tries
something doesn't prove that it will always work like that...
>
got any more bright ideas?
>
Or is the question to hard for you?

No, the question is not to (sic) hard for me. But, as you've already
discovered, it isn't that difficult to test, either.

[Jerry Stuckle]

Re: safe to delete elements of array in foreach

ZeldorBlat wrote:

On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
wrote:

>"ZeldorBlat " <zeldorb...@gma il.comwrote in message
>>
>news:117950101 8.125313.63600@ p77g2000hsh.goo glegroups.com.. .
>>

>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>wrote:
>>>Is it safe to remove elements from an array that foreach is working on?
>>>(normally this is not the case but not sure in php) If so is there an
>>>efficient way to handle it? (I could add the indexes to a temp array and
>>>delete afterwards if necessary but since I'm actually working in a nested
>>>situation this could get a little messy. I guess I could set there values
>>>to
>>>null and remove them afterwards?
>>>Thanks,
>>>Jon
>>Why don't you try it and see what happens?

>Um... cause I did... but that doesn't mean much. Just cause someone tries
>something doesn't prove that it will always work like that...
>>
>got any more bright ideas?
>>
>Or is the question to hard for you?

>
No, the question is not to (sic) hard for me. But, as you've already
discovered, it isn't that difficult to test, either.
>

Sorry, I agree with Jon on this one.

I make it a habit not to delete entries in a foreach() loop. Rather, I
build an array of keys I want to delete, and after the loop ends, delete
the entries from my delete array.

I don't know whether an operation like this is guaranteed to work in PHP
- I've never seen it documented, so I suspect not. And just because it
works in one release under a certain set of conditions is not a
guarantee it will work on another release or under different conditions.


--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[ZeldorBlat]

Re: safe to delete elements of array in foreach

On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

ZeldorBlat wrote:

On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
wrote:

"ZeldorBlat " <zeldorb...@gma il.comwrote in message

>

>news:117950101 8.125313.63600@ p77g2000hsh.goo glegroups.com.. .

>

>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>wrote:
>>Is it safe to remove elements from an array that foreach is working on?
>>(normally this is not the case but not sure in php) If so is there an
>>efficient way to handle it? (I could add the indexes to a temp array and
>>delete afterwards if necessary but since I'm actually working in a nested
>>situation this could get a little messy. I guess I could set there values
>>to
>>null and remove them afterwards?
>>Thanks,
>>Jon
>Why don't you try it and see what happens?
Um... cause I did... but that doesn't mean much. Just cause someone tries
something doesn't prove that it will always work like that...

>

got any more bright ideas?

>

Or is the question to hard for you?

>

No, the question is not to (sic) hard for me. But, as you've already
discovered, it isn't that difficult to test, either.

>
Sorry, I agree with Jon on this one.
>
I make it a habit not to delete entries in a foreach() loop. Rather, I
build an array of keys I want to delete, and after the loop ends, delete
the entries from my delete array.
>
I don't know whether an operation like this is guaranteed to work in PHP
- I've never seen it documented, so I suspect not. And just because it
works in one release under a certain set of conditions is not a
guarantee it will work on another release or under different conditions.
>
--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstuck...@attgl obal.net
=============== ===

I never said I disagreed with him -- in fact I, too, generally don't
delete elements inside a foreach. However, I will say that when I
have done it things seem to work as expected. I guess it all comes
down to whether or not the array's internal pointer is modified when
you unset the element it's pointing to (I suspect it isn't).

I see a lot of questions in these newsgroups that look something like,
"What happens if I do X?" or "In PHP is this code valid?" The point I
was trying to make (and apparently Jon took offense to it) was that
it's easy enough to just try it and see what happens. Software is
just that: soft. It can be changed easily enough :)

[Jerry Stuckle]

Re: safe to delete elements of array in foreach

ZeldorBlat wrote:

On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

>ZeldorBlat wrote:

>>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>wrote:
>>>"ZeldorBla t" <zeldorb...@gma il.comwrote in message
>>>news:1179501 018.125313.6360 0@p77g2000hsh.g ooglegroups.com ...
>>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>wrote:
>>>>>Is it safe to remove elements from an array that foreach is working on?
>>>>>(normall y this is not the case but not sure in php) If so is there an
>>>>>efficien t way to handle it? (I could add the indexes to a temp array and
>>>>>delete afterwards if necessary but since I'm actually working in a nested
>>>>>situatio n this could get a little messy. I guess I could set there values
>>>>>to
>>>>>null and remove them afterwards?
>>>>>Thanks,
>>>>>Jon
>>>>Why don't you try it and see what happens?
>>>Um... cause I did... but that doesn't mean much. Just cause someone tries
>>>something doesn't prove that it will always work like that...
>>>got any more bright ideas?
>>>Or is the question to hard for you?
>>No, the question is not to (sic) hard for me. But, as you've already
>>discovered, it isn't that difficult to test, either.

>Sorry, I agree with Jon on this one.
>>
>I make it a habit not to delete entries in a foreach() loop. Rather, I
>build an array of keys I want to delete, and after the loop ends, delete
>the entries from my delete array.
>>
>I don't know whether an operation like this is guaranteed to work in PHP
>- I've never seen it documented, so I suspect not. And just because it
>works in one release under a certain set of conditions is not a
>guarantee it will work on another release or under different conditions.
>>
>--
>============== ====
>Remove the "x" from my email address
>Jerry Stuckle
>JDS Computer Training Corp.
>jstuck...@attg lobal.net
>============== ====

>
I never said I disagreed with him -- in fact I, too, generally don't
delete elements inside a foreach. However, I will say that when I
have done it things seem to work as expected. I guess it all comes
down to whether or not the array's internal pointer is modified when
you unset the element it's pointing to (I suspect it isn't).
>
I see a lot of questions in these newsgroups that look something like,
"What happens if I do X?" or "In PHP is this code valid?" The point I
was trying to make (and apparently Jon took offense to it) was that
it's easy enough to just try it and see what happens. Software is
just that: soft. It can be changed easily enough :)
>
>

Yes, and in a case like this that change can break his code.

As I said - I've never seen it documented that this is valid. Maybe it
is and I missed it; I really don't know.

But this isn't the same as a lot of other "try it and find out"
questions. In this case it's a known problem in other programming
languages, and if it is documented that this should or should not work,
no one has pointed anyone to it.

And until I see something from the PHP developers saying it is OK, I
wouldn't do it.

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[ZeldorBlat]

Re: safe to delete elements of array in foreach

On May 18, 10:44 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

ZeldorBlat wrote:

On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

ZeldorBlat wrote:
>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>wrote:
>>"ZeldorBlat " <zeldorb...@gma il.comwrote in message
>>>news:1179501 018.125313.6360 0@p77g2000hsh.g ooglegroups.com ...
>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>wrote:
>>>>Is it safe to remove elements from an array that foreach is working on?
>>>>(normally this is not the case but not sure in php) If so is there an
>>>>efficient way to handle it? (I could add the indexes to a temp array and
>>>>delete afterwards if necessary but since I'm actually working in a nested
>>>>situation this could get a little messy. I guess I could set there values
>>>>to
>>>>null and remove them afterwards?
>>>>Thanks,
>>>>Jon
>>>Why don't you try it and see what happens?
>>Um... cause I did... but that doesn't mean much. Just cause someone tries
>>something doesn't prove that it will always work like that...
>>got any more bright ideas?
>>Or is the question to hard for you?
>No, the question is not to (sic) hard for me. But, as you've already
>discovered, it isn't that difficult to test, either.
Sorry, I agree with Jon on this one.

>

I make it a habit not to delete entries in a foreach() loop. Rather, I
build an array of keys I want to delete, and after the loop ends, delete
the entries from my delete array.

>

I don't know whether an operation like this is guaranteed to work in PHP
- I've never seen it documented, so I suspect not. And just because it
works in one release under a certain set of conditions is not a
guarantee it will work on another release or under different conditions.

>

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstuck...@attgl obal.net
=============== ===

>

I never said I disagreed with him -- in fact I, too, generally don't
delete elements inside a foreach. However, I will say that when I
have done it things seem to work as expected. I guess it all comes
down to whether or not the array's internal pointer is modified when
you unset the element it's pointing to (I suspect it isn't).

>

I see a lot of questions in these newsgroups that look something like,
"What happens if I do X?" or "In PHP is this code valid?" The point I
was trying to make (and apparently Jon took offense to it) was that
it's easy enough to just try it and see what happens. Software is
just that: soft. It can be changed easily enough :)

>
Yes, and in a case like this that change can break his code.
>
As I said - I've never seen it documented that this is valid. Maybe it
is and I missed it; I really don't know.
>
But this isn't the same as a lot of other "try it and find out"
questions. In this case it's a known problem in other programming
languages, and if it is documented that this should or should not work,
no one has pointed anyone to it.
>
And until I see something from the PHP developers saying it is OK, I
wouldn't do it.
>
--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstuck...@attgl obal.net
=============== ===

This suggests that it's safe (from <http://www.php.net/foreach>):

"Unless the array is referenced, foreach operates on a copy of the
specified array and not the array itself. Therefore, the array pointer
is not modified as with the each() construct, and changes to the array
element returned are not reflected in the original array."

So unsetting a value in the original array should not affect the copy
that foreach is working on.

[Rami Elomaa]

Re: safe to delete elements of array in foreach

Jon Slaughter kirjoitti:

Is it safe to remove elements from an array that foreach is working on?
(normally this is not the case but not sure in php) If so is there an
efficient way to handle it? (I could add the indexes to a temp array and
delete afterwards if necessary but since I'm actually working in a nested
situation this could get a little messy. I guess I could set there values to
null and remove them afterwards?

$a = range(0,10);
foreach($a as $key =$val)
if($val%2)
unset($a[$key]);

I've done something like this and have never had any problems. I don't
see the threats in this kind of thing, can you explain me what you think
that might be unsafe in this method?

--
Rami.Elomaa@gma il.com

"Wikipedia on vähän niinq internetin raamattu, kukaan ei pohjimmiltaan
usko siihen ja kukaan ei tiedä mikä pitää paikkansa." -- z00ze

[Schraalhans Keukenmeester]

Re: safe to delete elements of array in foreach

At Fri, 18 May 2007 21:05:36 -0400, Jerry Stuckle let his monkeys type:

ZeldorBlat wrote:

>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>wrote:

>>"ZeldorBlat " <zeldorb...@gma il.comwrote in message
>>>
>>news:11795010 18.125313.63600 @p77g2000hsh.go oglegroups.com. ..
>>>
>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>wrote:
>>>>Is it safe to remove elements from an array that foreach is working on?
>>>>(normally this is not the case but not sure in php) If so is there an
>>>>efficient way to handle it? (I could add the indexes to a temp array and
>>>>delete afterwards if necessary but since I'm actually working in a nested
>>>>situation this could get a little messy. I guess I could set there values
>>>>to
>>>>null and remove them afterwards?
>>>>Thanks,
>>>>Jon
>>>Why don't you try it and see what happens?
>>Um... cause I did... but that doesn't mean much. Just cause someone tries
>>something doesn't prove that it will always work like that...
>>>
>>got any more bright ideas?
>>>
>>Or is the question to hard for you?

>>
>No, the question is not to (sic) hard for me. But, as you've already
>discovered, it isn't that difficult to test, either.
>>

>
Sorry, I agree with Jon on this one.
>
I make it a habit not to delete entries in a foreach() loop. Rather, I
build an array of keys I want to delete, and after the loop ends, delete
the entries from my delete array.
>
I don't know whether an operation like this is guaranteed to work in PHP
- I've never seen it documented, so I suspect not. And just because it
works in one release under a certain set of conditions is not a
guarantee it will work on another release or under different conditions.

I agree 100% with you not to rely on undocumented 'features'.
Just out of curiosity I took this one step further and discovered the
following (again, can't rely on this to hold true unless it's documented
somewhere, well hidden):

<?PHP
$array=array('j ohn','james','d elilah','mary') ;
foreach ($array as $key=>$value) {
echo "$key =$value".NEWLIN E;
if ($value == 'delilah') {
$array[$key]='samson';
}
elseif ($value=='james ') {
unset($array[$key]);
}
}
echo NEWLINE;
foreach ($array as $key=>$value) {
echo "$key =$value".NEWLIN E;
}
?>
0 =john
1 =james
2 =delilah
3 =mary

0 =john
2 =samson
3 =mary

The foreach loop operates on a copy of the array
The original array remains in scope
Current($array) points to the first element throughout the loop

I'd think setting elements to NULL directly in the array isn't any better,
you're still relying on the same 'feature'.

Sh

[Schraalhans Keukenmeester]

Re: safe to delete elements of array in foreach

At Fri, 18 May 2007 20:10:57 -0700, ZeldorBlat let his monkeys type:

>============== ====

>
This suggests that it's safe (from <http://www.php.net/foreach>):
>
"Unless the array is referenced, foreach operates on a copy of the
specified array and not the array itself. Therefore, the array pointer
is not modified as with the each() construct, and changes to the array
element returned are not reflected in the original array."
>

Okay, well, uhmmm, not so well hidden then.

Try unsetting and/or changing values in a referenced array foreach:
You might not end u with what you expect. I repeated the code in my other
reply, now operating on $value directly:

$array=array('j ohn','james','d elilah','mary') ;
foreach ($array as $key=>&$value) {
if ($value == 'delilah') {
$value ='samson';
}
elseif ($value=='james ') {
$value = null;;
}
echo "$key =$value".NEWLIN E;
}

foreach ($array as $key=>$value) {
echo "$key =$value".NEWLIN E;
}
Output:
0 =john
1 =>
2 =samson
3 =mary
0 =john
1 =>
2 =samson
3 =samson // !!!

Must be some logic for this, but I fail to see it right now.

Sh.

[Jon Slaughter]

Re: safe to delete elements of array in foreach


"ZeldorBlat " <zeldorblat@gma il.comwrote in message
news:1179544257 .218638.219550@ u30g2000hsc.goo glegroups.com.. .

On May 18, 10:44 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

>ZeldorBlat wrote:

On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:
>ZeldorBlat wrote:
>>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>wrote:
>>>"ZeldorBla t" <zeldorb...@gma il.comwrote in message
>>>>news:117950 1018.125313.636 00@p77g2000hsh. googlegroups.co m...
>>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>wrote:
>>>>>Is it safe to remove elements from an array that foreach is
>>>>>working on?
>>>>>(normall y this is not the case but not sure in php) If so is there
>>>>>an
>>>>>efficien t way to handle it? (I could add the indexes to a temp
>>>>>array and
>>>>>delete afterwards if necessary but since I'm actually working in a
>>>>>nested
>>>>>situatio n this could get a little messy. I guess I could set there
>>>>>values
>>>>>to
>>>>>null and remove them afterwards?
>>>>>Thanks,
>>>>>Jon
>>>>Why don't you try it and see what happens?
>>>Um... cause I did... but that doesn't mean much. Just cause someone
>>>tries
>>>something doesn't prove that it will always work like that...
>>>got any more bright ideas?
>>>Or is the question to hard for you?
>>No, the question is not to (sic) hard for me. But, as you've already
>>discovered, it isn't that difficult to test, either.
>Sorry, I agree with Jon on this one.

>>

>I make it a habit not to delete entries in a foreach() loop. Rather,
>I
>build an array of keys I want to delete, and after the loop ends,
>delete
>the entries from my delete array.

>>

>I don't know whether an operation like this is guaranteed to work in
>PHP
>- I've never seen it documented, so I suspect not. And just because
>it
>works in one release under a certain set of conditions is not a
>guarantee it will work on another release or under different
>conditions.

>>

>--
>============== ====
>Remove the "x" from my email address
>Jerry Stuckle
>JDS Computer Training Corp.
>jstuck...@attg lobal.net
>============== ====

>>

I never said I disagreed with him -- in fact I, too, generally don't
delete elements inside a foreach. However, I will say that when I
have done it things seem to work as expected. I guess it all comes
down to whether or not the array's internal pointer is modified when
you unset the element it's pointing to (I suspect it isn't).

>>

I see a lot of questions in these newsgroups that look something like,
"What happens if I do X?" or "In PHP is this code valid?" The point I
was trying to make (and apparently Jon took offense to it) was that
it's easy enough to just try it and see what happens. Software is
just that: soft. It can be changed easily enough :)

>>
>Yes, and in a case like this that change can break his code.
>>
>As I said - I've never seen it documented that this is valid. Maybe it
>is and I missed it; I really don't know.
>>
>But this isn't the same as a lot of other "try it and find out"
>questions. In this case it's a known problem in other programming
>languages, and if it is documented that this should or should not work,
>no one has pointed anyone to it.
>>
>And until I see something from the PHP developers saying it is OK, I
>wouldn't do it.
>>
>--
>============== ====
>Remove the "x" from my email address
>Jerry Stuckle
>JDS Computer Training Corp.
>jstuck...@attg lobal.net
>============== ====

>
This suggests that it's safe (from <http://www.php.net/foreach>):
>
"Unless the array is referenced, foreach operates on a copy of the
specified array and not the array itself. Therefore, the array pointer
is not modified as with the each() construct, and changes to the array
element returned are not reflected in the original array."
>
So unsetting a value in the original array should not affect the copy
that foreach is working on.

Your right. I saw this after the fact after I did try it out and compared it
with a for loop. The foreach worked while the for loop didn't. Then I went
to the manual and saw that it worked on a copy.

So in this case it should work just fine. The for looped version actually
doesn't work and does give the problem I suspected. (thought I sent a post
a bout it though).

So unless they go change how foreach works in a newer version I think it
will be safe. I'm still trying to get used to php as it does a lot of things
differently than I'm used to.

The issue with "trying it out" is that in things like this you can't be sure
since its a implementation artifact... The only way to know is to know that
foreach is working on a copy. Of course maybe one could realize that by
doing a few examples but when usually one doesn't want to rely on what they
think is going on in this sorta situation and needs to know the facts.

Of course now I know its completely safe which was my original question ;)
It came from the manual which is where I should have looked in the fist
place(I did but I guess I skipped over that part ;/

Thanks,
Jon

[Jerry Stuckle]

Re: safe to delete elements of array in foreach

ZeldorBlat wrote:

On May 18, 10:44 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

>ZeldorBlat wrote:

>>On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:
>>>ZeldorBlat wrote:
>>>>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>wrote:
>>>>>"ZeldorBla t" <zeldorb...@gma il.comwrote in message
>>>>>news:11795 01018.125313.63 600@p77g2000hsh .googlegroups.c om...
>>>>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>>>wrote:
>>>>>>>Is it safe to remove elements from an array that foreach is working on?
>>>>>>>(normall y this is not the case but not sure in php) If so is there an
>>>>>>>efficien t way to handle it? (I could add the indexes to a temp array and
>>>>>>>delete afterwards if necessary but since I'm actually working in a nested
>>>>>>>situatio n this could get a little messy. I guess I could set there values
>>>>>>>to
>>>>>>>null and remove them afterwards?
>>>>>>>Thanks ,
>>>>>>>Jon
>>>>>>Why don't you try it and see what happens?
>>>>>Um... cause I did... but that doesn't mean much. Just cause someone tries
>>>>>somethin g doesn't prove that it will always work like that...
>>>>>got any more bright ideas?
>>>>>Or is the question to hard for you?
>>>>No, the question is not to (sic) hard for me. But, as you've already
>>>>discovere d, it isn't that difficult to test, either.
>>>Sorry, I agree with Jon on this one.
>>>I make it a habit not to delete entries in a foreach() loop. Rather, I
>>>build an array of keys I want to delete, and after the loop ends, delete
>>>the entries from my delete array.
>>>I don't know whether an operation like this is guaranteed to work in PHP
>>>- I've never seen it documented, so I suspect not. And just because it
>>>works in one release under a certain set of conditions is not a
>>>guarantee it will work on another release or under different conditions.
>>>--
>>>============ ======
>>>Remove the "x" from my email address
>>>Jerry Stuckle
>>>JDS Computer Training Corp.
>>>jstuck...@at tglobal.net
>>>============ ======
>>I never said I disagreed with him -- in fact I, too, generally don't
>>delete elements inside a foreach. However, I will say that when I
>>have done it things seem to work as expected. I guess it all comes
>>down to whether or not the array's internal pointer is modified when
>>you unset the element it's pointing to (I suspect it isn't).
>>I see a lot of questions in these newsgroups that look something like,
>>"What happens if I do X?" or "In PHP is this code valid?" The point I
>>was trying to make (and apparently Jon took offense to it) was that
>>it's easy enough to just try it and see what happens. Software is
>>just that: soft. It can be changed easily enough :)

>Yes, and in a case like this that change can break his code.
>>
>As I said - I've never seen it documented that this is valid. Maybe it
>is and I missed it; I really don't know.
>>
>But this isn't the same as a lot of other "try it and find out"
>questions. In this case it's a known problem in other programming
>languages, and if it is documented that this should or should not work,
>no one has pointed anyone to it.
>>
>And until I see something from the PHP developers saying it is OK, I
>wouldn't do it.
>>
>--
>============== ====
>Remove the "x" from my email address
>Jerry Stuckle
>JDS Computer Training Corp.
>jstuck...@attg lobal.net
>============== ====

>
This suggests that it's safe (from <http://www.php.net/foreach>):
>
"Unless the array is referenced, foreach operates on a copy of the
specified array and not the array itself. Therefore, the array pointer
is not modified as with the each() construct, and changes to the array
element returned are not reflected in the original array."
>
So unsetting a value in the original array should not affect the copy
that foreach is working on.
>

I read that as just the opposite - changes in the copy do not affect the
original array.

It doesn't say how often the copy is refreshed from the original array -
or when changes in the original are reflected in the copy.

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[Jerry Stuckle]

Re: safe to delete elements of array in foreach

Jon Slaughter wrote:

"ZeldorBlat " <zeldorblat@gma il.comwrote in message
news:1179544257 .218638.219550@ u30g2000hsc.goo glegroups.com.. .

>On May 18, 10:44 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:

>>ZeldorBlat wrote:
>>>On May 18, 9:05 pm, Jerry Stuckle <jstuck...@attg lobal.netwrote:
>>>>ZeldorBla t wrote:
>>>>>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>>wrote:
>>>>>>"ZeldorBl at" <zeldorb...@gma il.comwrote in message
>>>>>>news:1179 501018.125313.6 3600@p77g2000hs h.googlegroups. com...
>>>>>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>>>>wrote:
>>>>>>>>Is it safe to remove elements from an array that foreach is
>>>>>>>>worki ng on?
>>>>>>>>(normal ly this is not the case but not sure in php) If so is there
>>>>>>>>an
>>>>>>>>efficie nt way to handle it? (I could add the indexes to a temp
>>>>>>>>array and
>>>>>>>>delet e afterwards if necessary but since I'm actually working in a
>>>>>>>>neste d
>>>>>>>>situati on this could get a little messy. I guess I could set there
>>>>>>>>value s
>>>>>>>>to
>>>>>>>>null and remove them afterwards?
>>>>>>>>Thank s,
>>>>>>>>Jon
>>>>>>>Why don't you try it and see what happens?
>>>>>>Um... cause I did... but that doesn't mean much. Just cause someone
>>>>>>tries
>>>>>>somethi ng doesn't prove that it will always work like that...
>>>>>>got any more bright ideas?
>>>>>>Or is the question to hard for you?
>>>>>No, the question is not to (sic) hard for me. But, as you've already
>>>>>discovered , it isn't that difficult to test, either.
>>>>Sorry, I agree with Jon on this one.
>>>>I make it a habit not to delete entries in a foreach() loop. Rather,
>>>>I
>>>>build an array of keys I want to delete, and after the loop ends,
>>>>delete
>>>>the entries from my delete array.
>>>>I don't know whether an operation like this is guaranteed to work in
>>>>PHP
>>>>- I've never seen it documented, so I suspect not. And just because
>>>>it
>>>>works in one release under a certain set of conditions is not a
>>>>guarantee it will work on another release or under different
>>>>condition s.
>>>>--
>>>>=========== =======
>>>>Remove the "x" from my email address
>>>>Jerry Stuckle
>>>>JDS Computer Training Corp.
>>>>jstuck...@a ttglobal.net
>>>>=========== =======
>>>I never said I disagreed with him -- in fact I, too, generally don't
>>>delete elements inside a foreach. However, I will say that when I
>>>have done it things seem to work as expected. I guess it all comes
>>>down to whether or not the array's internal pointer is modified when
>>>you unset the element it's pointing to (I suspect it isn't).
>>>I see a lot of questions in these newsgroups that look something like,
>>>"What happens if I do X?" or "In PHP is this code valid?" The point I
>>>was trying to make (and apparently Jon took offense to it) was that
>>>it's easy enough to just try it and see what happens. Software is
>>>just that: soft. It can be changed easily enough :)
>>Yes, and in a case like this that change can break his code.
>>>
>>As I said - I've never seen it documented that this is valid. Maybe it
>>is and I missed it; I really don't know.
>>>
>>But this isn't the same as a lot of other "try it and find out"
>>questions. In this case it's a known problem in other programming
>>languages, and if it is documented that this should or should not work,
>>no one has pointed anyone to it.
>>>
>>And until I see something from the PHP developers saying it is OK, I
>>wouldn't do it.
>>>
>>--
>>============= =====
>>Remove the "x" from my email address
>>Jerry Stuckle
>>JDS Computer Training Corp.
>>jstuck...@att global.net
>>============= =====

>This suggests that it's safe (from <http://www.php.net/foreach>):
>>
>"Unless the array is referenced, foreach operates on a copy of the
>specified array and not the array itself. Therefore, the array pointer
>is not modified as with the each() construct, and changes to the array
>element returned are not reflected in the original array."
>>
>So unsetting a value in the original array should not affect the copy
>that foreach is working on.

>
>
Your right. I saw this after the fact after I did try it out and compared it
with a for loop. The foreach worked while the for loop didn't. Then I went
to the manual and saw that it worked on a copy.
>
So in this case it should work just fine. The for looped version actually
doesn't work and does give the problem I suspected. (thought I sent a post
a bout it though).
>
So unless they go change how foreach works in a newer version I think it
will be safe. I'm still trying to get used to php as it does a lot of things
differently than I'm used to.
>
The issue with "trying it out" is that in things like this you can't be sure
since its a implementation artifact... The only way to know is to know that
foreach is working on a copy. Of course maybe one could realize that by
doing a few examples but when usually one doesn't want to rely on what they
think is going on in this sorta situation and needs to know the facts.
>
Of course now I know its completely safe which was my original question ;)
It came from the manual which is where I should have looked in the fist
place(I did but I guess I skipped over that part ;/
>
Thanks,
Jon
>
>

Jon,

I disagree it's "completely safe". All this is saying is that the
changes to the copy will not affect the original. It says nothing about
what changes to the original will affect.

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[Jerry Stuckle]

Re: safe to delete elements of array in foreach

Schraalhans Keukenmeester wrote:

At Fri, 18 May 2007 21:05:36 -0400, Jerry Stuckle let his monkeys type:
>

>ZeldorBlat wrote:

>>On May 18, 11:40 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>wrote:
>>>"ZeldorBla t" <zeldorb...@gma il.comwrote in message
>>>>
>>>news:1179501 018.125313.6360 0@p77g2000hsh.g ooglegroups.com ...
>>>>
>>>>On May 18, 11:05 am, "Jon Slaughter" <Jon_Slaugh...@ Hotmail.com>
>>>>wrote:
>>>>>Is it safe to remove elements from an array that foreach is working on?
>>>>>(normall y this is not the case but not sure in php) If so is there an
>>>>>efficien t way to handle it? (I could add the indexes to a temp array and
>>>>>delete afterwards if necessary but since I'm actually working in a nested
>>>>>situatio n this could get a little messy. I guess I could set there values
>>>>>to
>>>>>null and remove them afterwards?
>>>>>Thanks,
>>>>>Jon
>>>>Why don't you try it and see what happens?
>>>Um... cause I did... but that doesn't mean much. Just cause someone tries
>>>something doesn't prove that it will always work like that...
>>>>
>>>got any more bright ideas?
>>>>
>>>Or is the question to hard for you?
>>No, the question is not to (sic) hard for me. But, as you've already
>>discovered, it isn't that difficult to test, either.
>>>

>Sorry, I agree with Jon on this one.
>>
>I make it a habit not to delete entries in a foreach() loop. Rather, I
>build an array of keys I want to delete, and after the loop ends, delete
>the entries from my delete array.
>>
>I don't know whether an operation like this is guaranteed to work in PHP
>- I've never seen it documented, so I suspect not. And just because it
>works in one release under a certain set of conditions is not a
>guarantee it will work on another release or under different conditions.

>
I agree 100% with you not to rely on undocumented 'features'.
Just out of curiosity I took this one step further and discovered the
following (again, can't rely on this to hold true unless it's documented
somewhere, well hidden):
>
<?PHP
$array=array('j ohn','james','d elilah','mary') ;
foreach ($array as $key=>$value) {
echo "$key =$value".NEWLIN E;
if ($value == 'delilah') {
$array[$key]='samson';
}
elseif ($value=='james ') {
unset($array[$key]);
}
}
echo NEWLINE;
foreach ($array as $key=>$value) {
echo "$key =$value".NEWLIN E;
}
?>
0 =john
1 =james
2 =delilah
3 =mary
>
0 =john
2 =samson
3 =mary
>
The foreach loop operates on a copy of the array
The original array remains in scope
Current($array) points to the first element throughout the loop
>
I'd think setting elements to NULL directly in the array isn't any better,
you're still relying on the same 'feature'.
>
Sh

Yes, foreach() works on a copy. But while the manual indicates changes
to the copy don't affect the original - they say nothing about when
changes to the original will affect the copy.

When I want to delete entries, I keep an array of keys to delete. When
I'm done with the array itself, I go through the second array and delete
all indicated keys.

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===