echo Carbon::today(); // 对象 2018-04-17 00:00:00
echo Carbon::tomorrow(); // 对象 2018-04-18 00:00:00
echo Carbon::yesterday();// 对象 2018-04-16 00:00:00
echo Carbon::today()->toDateTimeString(); // 字符串 2018-04-17 00:00:00
echo Carbon::yesterday()->toDateTimeString();// 字符串 2018-04-16 00:00:00
echo Carbon::tomorrow()->toDateTimeString(); // 字符串 2018-04-18 00:00:00
echo Carbon::today()->toDateString(); // 字符串 2018-04-17
echo Carbon::yesterday()->toDateString();// 字符串 2018-04-16
echo Carbon::tomorrow()->toDateString(); // 字符串 2018-04-18
echo Carbon::now()->startOfDay()->timestamp; // 1523980800
echo Carbon::now()->endOfDay()->timestamp; // 1524067199
echo Carbon::now()->startOfDay()->toDateTimeString(); // 2018-04-18 00:00:00
echo Carbon::now()->endOfDay()->toDateTimeString(); // 2018-04-18 23:59:59
echo Carbon::now()->startOfWeek()->timestamp; // 1523808000
echo Carbon::now()->endOfWeek()->timestamp; // 1524412799
echo Carbon::now()->startOfWeek()->toDateTimeString();// 2018-04-16 00:00:00
echo Carbon::now()->endOfWeek()->toDateTimeString();// 2018-04-22 23:59:59