- mktime: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$x1 = strtotime('00-00-00 00:00:00');
$x2 = strtotime('0000-00-00 00:00:00');
$x3 = 0;
$x4 = mktime(0, 0, 0, 0, 0, 0);
echo date (DATE_RFC2822, $x1)."\n";
echo date (DATE_RFC2822, $x2)."\n";
echo date (DATE_RFC2822, $x3)."\n";
echo date (DATE_RFC2822, $x4)."\n";