usort()

usort() — Sort an array by values using a user-defined comparison function.

Built-in function of PHP 8.5. The manual lists it as available in PHP 4, PHP 5, PHP 7, PHP 8. This page is the reference card: signature, parameters and return value, plus the changelog and the example the manual provides.

What it does

Sorts array in place by values using a user-supplied comparison function to determine the order.

Signature

usort(array &$array, callable $callback): true callback(mixed $a, mixed $b): int

Parameters

Parameter	Type	What it takes
&$array	array	The input array.
$callback	callable	The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

Return value

Always returns true.

Example

A runnable snippet:

function cmp($a, $b) { if ($a == $b) { return 0; } return ($a < $b) ? -1 : 1; } $a = array(3, 2, 5, 6, 1); usort($a, "cmp"); foreach ($a as $key => $value) { echo "$key: $value\n"; }

Output:

0: 1 1: 2 2: 3 3: 5 4: 6

Changelog

Version	Change
8.2.0	The return type is true now; previously, it was bool.
8.0.0	If callback expects a parameter to be passed by reference, this function will now emit an E_WARNING.