DOMNode children iteration (was Re: array() returns something weird)
| From: | Szczepan Hołyszewski | Date: | Mon, 24 Aug 2009 23:22:24 +0000 |
| Subject: | DOMNode children iteration (was Re: array() returns something weird) | ||
| References: | 1 2 3 | Groups: | php.general |
| Request: | Send a blank email to php-general+get-297155@lists.php.net to get a copy of this message | ||
Hi Lars and list!
New facts about the strange bug initially diagnosed as array() returning NULL:
Firstly, the issue is not really about array() returning null, but about full
blown UndefinedBehavior(TM) progressively trashing local variables. It just so
happened that I noticed it first with a variable to which array() had been
assigned just before things began breaking.
Secondly, I proudly present the culprit: things break when I iterate over a
DOMNode's children *by reference* using firstChild and nextSibling:
for($child=&$node->firstChild; $child; $child=&$child->nextSibling) {
//processing...
}
No problems if iteration is done by value or by DOMNodeList (childNodes,
DOMXPath...).
HOWEVER,
I still consider this a bug because it destablizes PHP. After the evil loop
has finished, things happen that should never happen, like a variable being
NULL immediately after being assigned array().
I attach a demonstration. It is a self-contained commented script that you can
execute from command line. Also attached is output on my machine.
Best regards,
Szczepan Hołyszewski
Attachment: [application/x-php] testme.php
THE GOOD WAY (DOMNodeList): Recursion structure: ->render() ->render() ->render() <- ->render() <- <- <- Transformation result: Some text. [object type='foo' name='bar'][param name='__default_content'] Some parameter text. Some parameter text. [object type='bar' name='nested'][param name='__default_content'] Some nested parameter text. Some nested parameter text. [object type='baz' name='deeply_nested'][param name='__default_content'] [/param][param name='bold']true[/param][/object] More nested parameter text More nested parameter text [/param][/object] [/param][/object] Some more text Success! THE MIXED WAY (DOMNodeList at outermost level, then firstChild/nextSibling by ref): Recursion structure: ->render() ->render() ->render() <- ->render() <- <- <- Transformation result: Some text. [object type='foo' name='bar'][param name='__default_content'] Some parameter text. Some parameter text. __default_content[param name='__default_content']__default_content[/param][/object] [/param][/object] Some more text Is it really a success? THE EVIL WAY (firstChild/nextSibling by ref): Recursion structure: ->render() ->render() ->render() <- ->render() <-
Attachment: [application/x-php] testme.php
THE GOOD WAY (DOMNodeList): Recursion structure: ->render() ->render() ->render() <- ->render() <- <- <- Transformation result: Some text. [object type='foo' name='bar'][param name='__default_content'] Some parameter text. Some parameter text. [object type='bar' name='nested'][param name='__default_content'] Some nested parameter text. Some nested parameter text. [object type='baz' name='deeply_nested'][param name='__default_content'] [/param][param name='bold']true[/param][/object] More nested parameter text More nested parameter text [/param][/object] [/param][/object] Some more text Success! THE MIXED WAY (DOMNodeList at outermost level, then firstChild/nextSibling by ref): Recursion structure: ->render() ->render() ->render() <- ->render() <- <- <- Transformation result: Some text. [object type='foo' name='bar'][param name='__default_content'] Some parameter text. Some parameter text. __default_content[param name='__default_content']__default_content[/param][/object] [/param][/object] Some more text Is it really a success? THE EVIL WAY (firstChild/nextSibling by ref): Recursion structure: ->render() ->render() ->render() <- ->render() <-