<?php
function bool_str($b)
{
return ($b ? "true" : "false");
}
function foo($first, &$second = null)
{
echo bool_str(isset($first)) . " " . bool_str(isset($second)) . " " .
bool_str(is_null($first)) . " " . bool_str(is_null($second)) . "\n";
}
$a = 1;
$b = 2;
foo($a, $b);
foo($a);
?>