For gurus: bug in php? Recursive foreach dont work properly.

[Tamagafk]

Hi! Looks like there is a bug in php. If I have function which uses
foreach to run trough array recursively, the lop-level foreach
interupted by lover-level foreach'es. If I use simply 'for' everything
is ok. Example:

I have an array of 3 objects connected hierarchically by their
variables id and parentId, here is the hierarchy:
id=1 parentId=0
....id=2 parentId=1
....id=3 parentId=1

I start digging from item with id=1 down to its chils and top-level
foreach NEVER REACH ELEMENT 3!!! Top-level foreach just stops.

<?php
function prn($s){
echo($s.'<br>') ;
}

$nodes = array();
$nodes[0] = new node(1, 0);
$nodes[1] = new node(2, 1);
$nodes[2] = new node(3, 1);
$nodes[3] = new node(4, 0);

class node{
var $id;
var $parentId;

function node($id, $parentId){
$this->id = $id;
$this->parentId = $parentId;
}

function dig($level){
global $nodes;

$l = '';
for($i=0; $i<$level; $i++) $l.='..';
prn($l.'looking for childs of '.$this->id.' {');

foreach($nodes as $n){
prn($l.$n->id.' (parent '.$n->parentId.')' );
if($n->parentId == $this->id){
$n->dig($level+1 );
}
}

prn($l.'}');
}

}

$nodes[0]->dig(0);

?>

The output should look like this:

looking for childs of 1 {
1 (parent 0)
2 (parent 1)
...looking for childs of 2 {
...1 (parent 0)
...2 (parent 1)
...3 (parent 1)
...}
3 (parent 1)
...looking for childs of 3 {
...1 (parent 0)
...2 (parent 1)
...3 (parent 1)
...}
}

But it looks like this:

looking for childs of 1 {
1 (parent 0)
2 (parent 1)
...looking for childs of 2 {
...1 (parent 0)
...2 (parent 1)
...3 (parent 1)
...}
}

[Tamagafk]

One more thing: pretend that there is no $nodes[3] = new node(4, 0);
:)

[Toby A Inkster]

Tamagafk wrote:

Hi! Looks like there is a bug in php. If I have function which uses
foreach to run trough array recursively, the lop-level foreach
interupted by lover-level foreach'es. If I use simply 'for' everything
is ok.

It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the "current"
element of array. foreach() uses this pointer to iterate through the
array. This is alluded to in the manual:

"the internal pointer of the original array *is*
advanced with the processing of the array."

So both foreach() functions are playing with the same internal pointer,
and screw things up for each other.

As an aside, you can use this internal pointer yourself via the following
functions:

each() - Returns current key, value pair
key() - Returns current key
current() - Returns current value
reset() - Reset pointer to start, return value
next() - Move pointer forwards, return value
prev() - Move pointer backwards, return value
end() - Move pointer to end, return value

Anyway, one solution is to either use for(), as you've discovered. This
works because instead of using PHP's internal array pointer to keep track
of your position in the array, you've defined your own pointer.

The other solution is to make a local copy of the array and run your
foreach() loop on that. Using for() is probably neater though.

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact
Geek of ~ HTML/SQL/Perl/PHP/Python*/Apache/Linux

* = I'm getting there!

[Vince Morgan]

"Toby A Inkster" <us**********@t obyinkster.co.u kwrote in message
news:gr******** ****@ophelia.g5 n.co.uk...

Tamagafk wrote:

Hi! Looks like there is a bug in php. If I have function which uses
foreach to run trough array recursively, the lop-level foreach
interupted by lover-level foreach'es. If I use simply 'for' everything
is ok.

It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the "current"

Why not in the "C sense"?
Something similar to an itterator in C++ ?

TIA
Vince

[Rami Elomaa]

Vince Morgan kirjoitti:

"Toby A Inkster" <us**********@t obyinkster.co.u kwrote in message
news:gr******** ****@ophelia.g5 n.co.uk...

>Tamagafk wrote:

>>Hi! Looks like there is a bug in php. If I have function which uses
foreach to run trough array recursively, the lop-level foreach
interupted by lover-level foreach'es. If I use simply 'for' everything
is ok.

It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the "current"

Why not in the "C sense"?

Well it's not like a pointer in C. In C your basic arrays (or strings
which are just arrays of characters) are pointers to memory locations,
and the index is an offset. Since PHP works at a higher level, it
doesn't know anything about the memory, so pointers in that sense don't
exist in php. However the datastructure of an array has an internal
"pointer" but it doesn't mean the same as pointers in C.

See http://en.wikipedia.org/wiki/Pointer_%28computing%29

--
Ra*********@gma il.com

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

[Jerry Stuckle]

Vince Morgan wrote:

"Toby A Inkster" <us**********@t obyinkster.co.u kwrote in message
news:gr******** ****@ophelia.g5 n.co.uk...

>Tamagafk wrote:

>>Hi! Looks like there is a bug in php. If I have function which uses
foreach to run trough array recursively, the lop-level foreach
interupted by lover-level foreach'es. If I use simply 'for' everything
is ok.

It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the "current"

Why not in the "C sense"?
Something similar to an itterator in C++ ?

TIA
Vince

Vince,

Because in C a pointer is a memory location. It's not in PHP - just an
indicator to the current location in an array.

And no, it's not like an iterator - there are no methods you can use on
the internal pointer - only the array itself.

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

[Rami Elomaa]

Jerry Stuckle kirjoitti:

And no, it's not like an iterator - there are no methods you can use on
the internal pointer - only the array itself.

Sigh... In the previous post Toby listed all the methods that can be
used on the internal pointer... So there are indeed methods for
manipulating the internal pointer, but the internal pointer is not like
an iterator in C++. :)

--
Ra*********@gma il.com

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

[Toby A Inkster]

Vince Morgan wrote:

Toby A Inkster wrote:

>It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the "current"

Why not in the "C sense"?

A pointer in the C sense of the word is (more or less) an exact memory
address for a piece of data.

The internal pointer in a PHP array has a far more ethereal nature.
Exactly how it works is an enigma wrapped in a riddle and shrouded by
mystery. We don't have direct access to the pointer, but can see its
ghostly effects in the list of functions I mentioned in my previous
post.

It's exact implementation in the PHP source code may well be as a C
pointer, but that doesn't (and shouldn't) matter to a person who's using
PHP arrays. The internal implementation as might well change for each new
version of PHP which is released -- as far as they're concerned, it
doesn't matter, as long as each(), next() and so on keep working as they
do.

Something similar to an itterator in C++ ?

The array is, yes.

PHP 5 has iterators too.

--
Toby A Inkster BSc (Hons) ARCS
Contact Me ~ http://tobyinkster.co.uk/contact
Geek of ~ HTML/SQL/Perl/PHP/Python*/Apache/Linux

* = I'm getting there!

[Vince Morgan]

"Vince Morgan" <vi****@REMOVEo ptusnet.com.auw rote in message
news:46******** **************@ news.optusnet.c om.au...

"Toby A Inkster" <us**********@t obyinkster.co.u kwrote in message
news:gr******** ****@ophelia.g5 n.co.uk...

Tamagafk wrote:

Hi! Looks like there is a bug in php. If I have function which uses
foreach to run trough array recursively, the lop-level foreach
interupted by lover-level foreach'es. If I use simply 'for' everything
is ok.

It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the "current"

Why not in the "C sense"?
Something similar to an itterator in C++ ?

TIA
Vince

I guess I didn't ask that q very well at all.
I'm familiar with pointers in C/C++, and iterators in C++, they are
languages I have most experience with.
However, I was thinking that they may be in some ways similar to say, a
vector iterator, without regard for methods etc.
I meant in a very general way, but I think it was probably a silly question
realy.
Trying to cheat my way into a greater understanding of the unerlying
implementation without doing the reading I guess ;)
Thank you for the reply though,
Regards,
Vince

[Vince Morgan]

"Toby A Inkster" <us**********@t obyinkster.co.u kwrote in message
news:iv******** ****@ophelia.g5 n.co.uk...

Vince Morgan wrote:

Toby A Inkster wrote:

It's not a bug -- it's a "feature". Internally, arrays in PHP have a
"pointer" (not in the C sense of the word) which points at the

"current"

Why not in the "C sense"?

A pointer in the C sense of the word is (more or less) an exact memory
address for a piece of data.

The internal pointer in a PHP array has a far more ethereal nature.
Exactly how it works is an enigma wrapped in a riddle and shrouded by
mystery. We don't have direct access to the pointer, but can see its
ghostly effects in the list of functions I mentioned in my previous
post.

Those functions had a sic "ghostly" likeness to a C++ vector and I was
wondering if in fact a vector may be used in the underlying implementation.

It's exact implementation in the PHP source code may well be as a C
pointer, but that doesn't (and shouldn't) matter to a person who's using
PHP arrays. The internal implementation as might well change for each new
version of PHP which is released -- as far as they're concerned, it
doesn't matter, as long as each(), next() and so on keep working as they
do.

My first problem in going from C to C++ was that I didn't "own" the pointers
of the library objects, so I appreciate what your saying here.

>

Something similar to an itterator in C++ ?

The array is, yes.

That's what I was imagining might be below the surface.

Thank you for taking the time Toby,

Vince