PHP之时间处理

面试的时候有一道题是这样的：封装一个函数实现，给你一个时间，输出这个时间的对应的这一天是星期几，其实无非就是一些时间格式的处理：

 date_default_timezone_set('PRC'); //默认时区
 $t = time();
 $today=date("Y-m-d",time());
 echo "今天：$today<br />";
 echo "某一天：".date("Y-m-d",strtotime("18 june 2008"))."<br />";
 echo "昨天：".date("Y-m-d",strtotime("-1 day"))."<br />";
 echo "明天：".date("Y-m-d",strtotime("+1 day"))."<br />";
 echo "一周后：".date("Y-m-d",strtotime("+1 week"))."<br />";
 echo "一周零两天四小时两秒后：".date("Y-m-d G：H：s",strtotime("+1 week 2 days 4 hours 2 seconds"))."<br />";
 echo "下个星期四：".date("Y-m-d",strtotime("next Thursday"))."<br />";
 echo "上个周一：".date("Y-m-d",strtotime("last Monday"))."<br />";
 echo "一个月前：".date("Y-m-d",strtotime("last month"))."<br />";
 echo "一个月后：".date("Y-m-d",strtotime("+1 month"))."<br />";
 echo "十年后：".date("Y-m-d",strtotime("+10 year"))."<br />";
 echo "<br />=======================================================<br /><br />";
 $w = date("w",time()); //获取今天是本周周几
 echo "今天是星期$w<br />";
 $d=array("日","一","二","三","四","五","六");
 $whatday="星期".$d[date("w",strtotime($today))]; //获取今天星期几
 echo "今天是$whatday<br />";
 $d0 = date("Y-m-d",strtotime("-$w day",$t)); //周开始
 echo "本周周日是：$d0<br />";
 $d6 = date("Y-m-d",strtotime((6-$w)." day",$t)); //周结束
 echo "本周周六是：$d6<br />";

 echo "本周周日是：".date("Y-m-d",strtotime("Sunday"))."<br />";  //周开始
 echo "本周周六是：".date("Y-m-d",strtotime("Saturday"))."<br />";  //周结束
 echo "上周周日是：".date("Y-m-d",strtotime("last Sunday"))."<br />";  //上周开始
 echo "上周周六是：".date("Y-m-d",strtotime("last Saturday"))."<br />";  //上周结束
 echo "<br />=======================================================<br /><br />";
 $time = abs((strtotime("2012-12-21") - strtotime(date("Y-m-d")))/86400);//获取两个日期之间的天数差
 echo "距离世界末日还有：$time 天<br />";  //上周结束