- var_dump: documentation ( source)
<?php
$dates = array(
'0001-12-31',
'1901-12-13',
'1901-12-14',
'1985-12-17',
'2012-1-19',
'2038-1-19',
'2038-1-20',
'9999-1-21',
);
echo "DateTime getTimestamp() format(\"U\")\n";
foreach ($dates as $date) {
$dt = new \DateTime($date);
var_dump($date, $dt->getTimestamp(), $dt->format("U"));
}