<?php
$values = [65, 63, 0x20AC, 128024];
foreach ($values as $value) {
var_dump(mb_chr($value, 'UTF-8'));
var_dump(mb_chr($value, 'ISO-8859-1'));
}
?>
string(1) "A"
string(1) "A"
string(1) "?"
string(1) "?"
string(3) "€"
bool(false)
string(4) ""
bool(false)