php获取指定月份的第一天开始和最后一天结束的时间戳

[code]<?php 
/**
 * 获取指定月份的第一天开始和最后一天结束的时间戳
 *
 * @param int $y 年份 $m 月份
 * @return array(本月开始时间，本月结束时间)
 */
function mFristAndLast($y = "", $m = ""){
    if ($y == "") $y = date("Y");
    if ($m == "") $m = date("m");
    $m = sprintf("%02d", intval($m));

    //填充字符串长度
    $y = str_pad(intval($y), 4, "0", STR_PAD_RIGHT);

    $m > 12 || $m < 1 ? $m = 1 : $m = $m;
    $firstday = strtotime($y . $m . "01000000");
    $firstdaystr = date("Y-m-01", $firstday);
    $lastday = strtotime(date('Y-m-d 23:59:59',   strtotime("$firstdaystr +1 month -1 day")));

    return array(
        "firstday" => $firstday,
        "lastday" => $lastday
    );
}

 ?>