From: php at sameprecision dot org
Operating system: irrelevant
PHP version: 5.2.6
PHP Bug Type: Arrays related
Bug description: usort assumes comparison operation is transitive
Description:
------------
Using usort, not all pairs of elements are compared. If a comparison
operation is not transitive, this leads to unexpected ordering, even though
every pair of elements are comparable.
This should probably be mentioned in the documentation.
Reproduce code:
---------------
//goal: sort $array so that an element is not a substring of any
subsequent elements
$array = array('aa','b','a');
//if $a is a substring of $b, return 1. Else return -1
function compare($a,$b){
return strpos($b,$a)===false ? -1 : 1;
}
usort($array,'compare');
print_r($array);
Expected result:
----------------
Array ( [0] => aa [1] => b [2] => a )
Actual result:
--------------
Array ( [0] => a [1] => b [2] => aa )
--
Edit bug report at http://bugs.php.net/?id=45988&edit=1
--
Try a CVS snapshot (PHP 5.2):
http://bugs.php.net/fix.php?id=45988&r=trysnapshot52
Try a CVS snapshot (PHP 5.3):
http://bugs.php.net/fix.php?id=45988&r=trysnapshot53
Try a CVS snapshot (PHP 6.0):
http://bugs.php.net/fix.php?id=45988&r=trysnapshot60
Fixed in CVS: http://bugs.php.net/fix.php?id=45988&r=fixedcvs
Fixed in release:
http://bugs.php.net/fix.php?id=45988&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=45988&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=45988&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=45988&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=45988&r=support
Expected behavior: http://bugs.php.net/fix.php?id=45988&r=notwrong
Not enough info:
http://bugs.php.net/fix.php?id=45988&r=notenoughinfo
Submitted twice:
http://bugs.php.net/fix.php?id=45988&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=45988&r=globals
PHP 4 support discontinued: http://bugs.php.net/fix.php?id=45988&r=php4
Daylight Savings: http://bugs.php.net/fix.php?id=45988&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=45988&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=45988&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=45988&r=float
No Zend Extensions: http://bugs.php.net/fix.php?id=45988&r=nozend
MySQL Configuration Error: http://bugs.php.net/fix.php?id=45988&r=mysqlcfg
