- printf: documentation ( source)
<?php
$array = array('a' => false, 'b' => null, 'c' => '', 'd' => 'd');
foreach ($array as $k => $v) {
printf(
'%s => %s isset = %s ake = %s',
$k, $v,
isset($array[ $k ]),
array_key_exists($k, $array)
);
}