$now = '2021-03-30';echo 'now： '.$now.'<br><br>';$firstDayOfThisMonth = date("Y-m-01", strtotime($now));echo 'first day of this month： '.$firstDayOfThisMonth.'<br><br>';$lastDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 day'));echo 'last day of prev month： '.$lastDayOfPrevMonth.'<br><br>';$firstDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 month'));echo 'first day of prev month： '.$firstDayOfPrevMonth.'<br><br>';echo '------------------------------------<br><br>';$now = '2021-10-01';echo 'now： '.$now.'<br><br>';$firstDayOfThisMonth = date("Y-m-01", strtotime($now));echo 'first day of this month： '.$firstDayOfThisMonth.'<br><br>';$lastDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 day'));echo 'last day of prev month： '.$lastDayOfPrevMonth.'<br><br>';$firstDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 month'));echo 'first day of prev month： '.$firstDayOfPrevMonth.'<br><br>';echo '------------------------------------<br><br>';$now = date("Y-m-d");echo 'now： '.$now.'<br><br>';$firstDayOfThisMonth = date("Y-m-01", strtotime($now));echo 'first day of this month： '.$firstDayOfThisMonth.'<br><br>';$lastDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 day'));echo 'last day of prev month： '.$lastDayOfPrevMonth.'<br><br>';$firstDayOfPrevMonth = date('Y-m-d', strtotime($firstDayOfThisMonth .' -1 month'));echo 'first day of prev month： '.$firstDayOfPrevMonth.'<br><br>';echo '------------------------------------<br><br>';**
测试后果
**
now： 2021-03-30
first day of this month： 2021-03-01
last day of prev month： 2021-02-28
first day of prev month： 2021-02-01
now： 2021-10-01
first day of this month： 2021-10-01
last day of prev month： 2021-09-30
first day of prev month： 2021-09-01
now： 2021-12-23
first day of this month： 2021-12-01
last day of prev month： 2021-11-30
first day of prev month： 2021-11-01