<?php

//獲取下月第一天

function getNextmonthFirstday($date) {

????$year = substr($date, 0, 4);

????$month = substr($date, 5, 2);

????$D = date('Y-m-d', mktime(0, 0, 0, $month + 1, 1, $year));

????return $D;

}

$last_month_first_day = getNextmonthFirstday("2017-11-01");//2017-10-01

//獲取所屬月的最后一天

$a = "2017-09-06";

date('Y-m-d', strtotime("$a +1 month -1 day"));