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：
1 date_default_timezone_set('PRC'); //默认时区 2 $t = time(); 3 $today=date("Y-m-d",time()); 4 echo "今天：$today<br />"; 5 echo "某一天：".date("Y-m-d",strtotime("18 june 2008"))."<br />"; 6 echo "昨天：".date("Y-m-d",strtotime("-1 day"))."<br />"; 7 echo "明天：".date("Y-m-d",strtotime("+1 day"))."<br />"; 8 echo "一周后：".date("Y-m-d",strtotime("+1 week"))."<br />"; 9 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 />"; 10 echo "下个星期四：".date("Y-m-d",strtotime("next Thursday"))."<br />"; 11 echo "上个周一：".date("Y-m-d",strtotime("last Monday"))."<br />"; 12 echo "一个月前：".date("Y-m-d",strtotime("last month"))."<br />"; 13 echo "一个月后：".date("Y-m-d",strtotime("+1 month"))."<br />"; 14 echo "十年后：".date("Y-m-d",strtotime("+10 year"))."<br />"; 15 echo "<br />=======================================================<br /><br />"; 16 $w = date("w",time()); //获取今天是本周周几 17 echo "今天是星期$w<br />"; 18 $d=array("日","一","二","三","四","五","六"); 19 $whatday="星期".$d[date("w",strtotime($today))]; //获取今天星期几 20 echo "今天是$whatday<br />"; 21 $d0 = date("Y-m-d",strtotime("-$w day",$t)); //周开始 22 echo "本周周日是：$d0<br />"; 23 $d6 = date("Y-m-d",strtotime((6-$w)." day",$t)); //周结束 24 echo "本周周六是：$d6<br />"; 25 26 echo "本周周日是：".date("Y-m-d",strtotime("Sunday"))."<br />"; //周开始 27 echo "本周周六是：".date("Y-m-d",strtotime("Saturday"))."<br />"; //周结束 28 echo "上周周日是：".date("Y-m-d",strtotime("last Sunday"))."<br />"; //上周开始 29 echo "上周周六是：".date("Y-m-d",strtotime("last Saturday"))."<br />"; //上周结束 30 echo "<br />=======================================================<br /><br />"; 31 $time = abs((strtotime("2012-12-21") - strtotime(date("Y-m-d")))/86400);//获取两个日期之间的天数差 32 echo "距离世界末日还有：$time 天<br />"; //上周结束 33