PHP array_multisort手动示例

Question

Why is 4 the first value in $ar2? I am pretty sure 4 should be at the end of the sorted array since its naturally sorting as SORT_ASC.

<?php
$ar1 = array(10, 100, 100, 0);
$ar2 = array(1, 3, 2, 4);
array_multisort($ar1, $ar2);

var_dump($ar1);
var_dump($ar2);
?>

In this example, after sorting, the first array will contain 0, 10, 100, 100. The second array will contain 4, 1, 2, 3. The entries in the second array corresponding to the identical entries in the first array (100 and 100) were sorted as well.

array(4) {
  [0]=> int(0)
  [1]=> int(10)
  [2]=> int(100)
  [3]=> int(100)
}
array(4) {
  [0]=> int(4)
  [1]=> int(1)
  [2]=> int(2)
  [3]=> int(3)
}

Answer 1

You already copied it form the manual:

In this example, after sorting, the first array will contain 0, 10, 100, 100. The second array will contain 4, 1, 2, 3. The entries in the second array corresponding to the identical entries in the first array (100 and 100) were sorted as well.

That means the second array is sorted by the order of the first array (the first array defines the order for the second array)

4 in $ar2 corresponds to 0 in $ar1. 0 is at the first position in $a1, hence 4 is the first in $ar2.