php獲取指定日期，前一天、前一周、前一個月、前一年，后一天，后一周，前一個月，前一年

dump(date('Y-m-d', strtotime('2018-10-1 +1 day')));

dump(date('Y-m-d', strtotime('2018-10-1 +1 week')));

dump(date('Y-m-d', strtotime('2018-10-1 +1 month')));

dump(date('Y-m-d', strtotime('2018-10-1 +1 year')));

dump(date('Y-m-d', strtotime('2018-10-1 -1 day')));

dump(date('Y-m-d', strtotime('2018-10-1 -1 week')));

dump(date('Y-m-d', strtotime('2018-10-1 -1 month')));

dump(date('Y-m-d', strtotime('2018-10-1 -1 year')));

同理，把2018-10-1換成變量，就可以做很多事了！

ps 由於每個月份的天數不一樣 +/- 1 month 特殊日期會有誤差

//獲取上一個月日期方法  

public function getBeforeMonthDate($currentDate)
{
    $currentMonthDay = date('t', strtotime($currentDate));
    $currentDay      = date('d', strtotime($currentDate));
    $yearMonth       = date('Y-m', strtotime($currentDate));
    $beforeMonth     = date('Y-m-d', strtotime("$yearMonth -1 month"));
    $beforeMonthDay  = date('t', strtotime($beforeMonth));
    if ($beforeMonthDay < $currentMonthDay && $beforeMonthDay < $currentDay) {
        $beforeDate = date("Y-m-d", strtotime("last day of -1 month", strtotime($currentDate)));
    } else {
        $beforeDate = date('Y-m-d', strtotime("$currentDate -1 month"));
    }
    return $beforeDate;
}