date的判定和加减

对事件对象的加减判定

<?php
$date = new DateTime('2000-01-01');
$date->add(new DateInterval('P10D'));
echo $date->format('Y-m-d') . "
";

//加减法也是一样的　

//date_sub($date,date_interval_create_from_date_string('10 days'));

 //$date->sub(new DateInterval('P10D'));

?> 

<?php
// Each set of intervals is equal.
$i = new DateInterval('P1D');
$i = DateInterval::createFromDateString('1 day');

$i = new DateInterval('P2W');
$i = DateInterval::createFromDateString('2 weeks');

$i = new DateInterval('P3M');
$i = DateInterval::createFromDateString('3 months');

$i = new DateInterval('P4Y');
$i = DateInterval::createFromDateString('4 years');

$i = new DateInterval('P1Y1D');
$i = DateInterval::createFromDateString('1 year + 1 day');

$i = new DateInterval('P1DT12H');
$i = DateInterval::createFromDateString('1 day + 12 hours');

$i = new DateInterval('PT3600S');
$i = DateInterval::createFromDateString('3600 seconds');
?>