PHP obtains the zero o'clock timestamp of the current day instance analysis

<?php
header("Content-type:text/html;charset=utf-8");
//设置北京时间为默认时区
date_default_timezone_set(&#39;PRC&#39;);
//输出当前时间
echo date("Y-m-d H:i:s",time()); //2016-08-11 10:30:32
//获得当日凌晨的时间戳
$today = strtotime(date("Y-m-d"),time());
echo &#39;<br>&#39;;
echo $today; //1470844800
echo &#39;<br>&#39;;
//验证当日凌晨的时间戳是否正确
echo date("Y-m-d H:i:s",$today); //2016-08-11 00:00:00
echo &#39;<br>&#39;;
//当天的24点时间戳
$end = $today+60*60*24;
//验证当天的24点时间戳是否正确
echo date("Y-m-d H:i:s", $end); //2016-08-12 00:00:00
echo &#39;<br>&#39;;
//获得指定时间的零点的时间戳
$time = strtotime(&#39;2014-06-06&#39;);
echo &#39;<br>&#39;;
echo $time; //1401984000
echo &#39;<br>&#39;;
//验证是否是指定时间的时间戳
echo date("Y-m-d H:i:s",$time); //2014-06-06 00:00:00
?>