[php]用PHP打印出前一天的时间格式

echo date("Y-m-d H:i:s",strtotime("-1 day"));

例子
<?php
echo(strtotime("now"));
echo(strtotime("3 October 2005"));
echo(strtotime("+5 hours"));
echo(strtotime("+1 week"));
echo(strtotime("+1 week 3 days 7 hours 5 seconds"));
echo(strtotime("next Monday"));
echo(strtotime("last Sunday"));
?>输出：

1138614504
1128290400
1138632504
1139219304
1139503709
1139180400
1138489200

$time=time();
//一天的开始
$start=strtotime(date('Y-m-d',$time).("-8 hours").'00:00:01');

echo date('Y-m-d H:i:s',$start);
//一天的结束
$end=strtotime(date('Y-m-d',$time).("-8 hours").'23:59:59');
echo date('Y-m-d H:i:s',$end);

$collection_of_products = Core::getModel('checkout/salesordergift')->getCollection()
->addFieldToSelect('gift_type')
->addFieldToSelect('created_at')
->addFieldToFilter('gift_type','bag')
->addFieldToFilter('created_at',array('from'=>$day_start,'to'=>$day_end));