#17307 [Opn->Csd]: sorting using usort() does not produce correct result anymore

ID: 17307 Updated by: joey@php.net Reported By: fcartegnie at nordnet dot fr -Status: Open +Status: Closed Bug Type: Arrays related Operating System: Linux PHP Version: 4.4.5 New Comment: Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://www.php.net/manual/ and the instructions on how to report a bug at http://bugs.php.net/how-to-report.php As is documented at php.net/usort: Note: If two members compare as equal, their order in the sorted array is undefined. Up to PHP 4.0.6 the user defined functions would keep the original order for those elements, but with the new sort algorithm introduced with 4.1.0 this is no longer the case as there is no solution to do so in an efficient way. Previous Comments: ------------------------------------------------------------------------ [2007-02-19 18:50:08] fcartegnie at nordnet dot fr Still broken on 4.4.5... Still using homemade usort routine for 4 years now. The usort functions really needs to be fixed ! Before usort()<br> Value: E<br> Value: C<br> Value: B<br> Value: D<br> Value: A<br> <p>After usort()<br> Value: A<br> Value: D<br> Value: B<br> Value: C<br> Value: E<br> ------------------------------------------------------------------------ [2002-06-26 08:12:55] david dot derr at milesmedia dot com Hi all. I think this is still a bug as I can partially recreate the behaviour that fcartegnie@nordnet.fr reported. On a script that uses a function passed to usort that always returns 0 (implying equal values), I am seeing that the order of elements in the array is being modified. The only reason I consider this a bug is because that was not the case in the earlier version I tested. Here are the details: -The code I used on both systems: <? //The function usort will use. Returns 0 implying that every comparison is equal. function fake_sort($left, $right){ return 0; } //create our aTest array and add some data to it $aTest = array(); $aTest[] = "E"; $aTest[] = "C"; $aTest[] = "B"; $aTest[] = "D"; $aTest[] = "A"; //output the order of elements in the array before running usort on it. reset($aTest); echo "Before usort()<br>\n"; while(list($key, $val) = each($aTest)){ echo "Value: ".$val."<br>\n"; } //sort it usort($aTest, "fake_sort"); //output the order of elements in the array after running usort on it. reset($aTest); echo "<p>After usort()<br>\n"; while(list($key, $val) = each($aTest)){ echo "Value: ".$val."<br>\n"; } ?> -Incorrect (unexpected) Results System: RH 7.2, Apache 1.3.26, PHP 4.2.1 Output: Before usort() Value: E Value: C Value: B Value: D Value: A After usort() Value: A Value: D Value: B Value: C Value: E -Correct (expected) Results System: RH 7.2, Apache 1.3.26, PHP 4.1.2 Output: Before usort() Value: E Value: C Value: B Value: D Value: A After usort() Value: E Value: C Value: B Value: D Value: A ------------------------------------------------------------------------ [2002-06-17 06:52:12] timebreaker at newmail dot ru Hi! It's really a problem. I tried to write simple ascending sort routine and got strange results too. Met the conditions at Intel P-133/Win98/Apache2.0.35/PPH4.2.0 and PHP4.2.1, it doesn't matter what the version is. In 4.0.6/4.1.x everything works... ------------------------------------------------------------------------ [2002-06-04 13:58:40] mfischer@php.net Heh, ok. Still better then a bug in PHP :) thx. ------------------------------------------------------------------------ [2002-06-04 13:44:21] mauf at franzoni dot info I fixed the problem in my sort routine... it works now (for 4.2.1, so far it seems it was 4.0.6 the buggy one as it has worked for a long while). So far there may be at most a backward compatibility issue (I still have to check back in 4.0.6) but it is no longer worth the critical status for sure... sorry for the bothering, cheers, mauro ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/17307 -- Edit this bug report at http://bugs.php.net/?id=17307&edit=1