note 109329 modified in function.usort by danbrown

From:	danbrown@php.net	Date:	Mon, 16 Jul 2012 15:45:09 +0000
Subject:	note 109329 modified in function.usort by danbrown
References:	1	Groups:	php.notes
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The usort function actually moves $b up when the callback function returns both 0 and 1. If you want to preserve the original order in the array, return 1 when $a == $b instead of 0. Try this code below to see how usort alters the order of the original array when all values are the same.

<?php
class TestObj {
 private $name;
 private $id;

 function TestObj($name, $id) {
 $this->name = $name;
 $this->id = $id;
 }

 static function cmp_obj($a, $b) {
 $al = strtolower($a->name);
 $bl = strtolower($b->name);
 if ($al == $bl) {
 return 0; // return 1 if you don't want $b to go in front of $a
 }
 return ($al > $bl) ? +1 : -1;
 }
}

$a[] = new TestObj("a", 1);
$a[] = new TestObj("a", 2);
$a[] = new TestObj("a", 3);

var_dump($a);
usort($a, array("TestObj", "cmp_obj"));
var_dump($a);
?> --was-- The usort function actually moves $b up when the callback function returns both 0 and 1. If you want to preserve the original order in the array, return 1 when $a == $b instead of 0. Try this code below to see how usort alters the order of the original array when all values are the same. <?php class TestObj { private $name; private $id; function TestObj($name, $id) { $this->name = $name; $this->id = $id; } static function cmp_obj($a, $b) { $al = strtolower($a->name); $bl = strtolower($b->name); if ($al == $bl) { return 0; // return 1 if you don't want $b to go in front of $a } return ($al > $bl) ? +1 : -1; } } $a[] = new TestObj("a", 1); $a[] = new TestObj("a", 2); $a[] = new TestObj("a", 3); var_dump($a); usort($a, array("TestObj", "cmp_obj")); var_dump($a); http://php.net/manual/en/function.usort.php