获取未来或过去某一天的时间

<?php
$date = new DateTime("2006-12-12");
$date->modify("+7 day");
echo $date->format("Y-m-d");
?>
<?php
// This is what you need for future date from now.
echo date('Y-m-d H:i:s', strtotime("+7 day"));

// This is what you need for future date from specific date.
echo date('Y-m-d H:i:s', strtotime('01/01/2010 +7 day'));
?>

<?php
# this gets you 7 days earlier than the current date
$lastWeek = mktime(0, 0, 0, date("m")  , date("d")-7, date("Y"));
# now pretty-print it out (eg, prints April 2, 2010.)
echo date("F j, Y.", $lastWeek), "\n";
?>