weirdest function with PHP

Question

alright, I'm trying something which should be like really easy.

Here it is:

usort($newarr, "cmp");

function cmp($a, $b)
{ return 0; }

The problem is simple: it does not sort the array by giving this warning message

Warning: usort() expects parameter 2 to be a valid callback, function 'cmp' not found or invalid function name

---

I have read this answer here PHP usort won't sort

but it just doesn't make any sense to me, I do not have a class like how it is explained in the answer 1 (and I don't even need any, i tried with $this, this, insted of "myclass" but it's simply not working any):

usort($items, array("MyClass", "compare_method"));

Answer 1

Change the script flow, by the time you are trying to sort your array cmp does not exists yet. So, this should work:

function cmp($a, $b)
{ return 0; }

usort($newarr, "cmp");

Answer 2

From the information you've posted with your question, it can not be specifically said why it does not work for you.

The code generally does work, it's perfectly alright (Demo):

<?php
$newarr = array();

if (!function_exists('cmp')) echo "cmp() not defined yet.\n";
usort($newarr, "cmp");

function cmp($a, $b)
{ return 0; }

I suggest you add more information to your question so it can be better said where the actual problem is located.

• Which PHP version are you using?
• Do you make use of namespaces?

Answer 3

Use the anonymous functions (or create_function) to create an anonymous function like your cmp, then pass it to usort.

Example:

usort($newarr, function($a, $b) {
    return 0;
});