【转】php周转日期，查询周的起始日期

function getWeekDate($year,$weeknum){
    $firstdayofyear=mktime(0,0,0,1,1,$year);
    $firstweekday=date('N',$firstdayofyear);
    $firstweenum=date('W',$firstdayofyear);
    if($firstweenum==1){
        $day=(1-($firstweekday-1))+7*($weeknum-1);
        $startdate=date('Y-m-d',mktime(0,0,0,1,$day,$year));
        $enddate=date('Y-m-d',mktime(0,0,0,1,$day+6,$year));
    }else{
        $day=(9-$firstweekday)+7*($weeknum-1);
        $startdate=date('Y-m-d',mktime(0,0,0,1,$day,$year));
        $enddate=date('Y-m-d',mktime(0,0,0,1,$day+6,$year));
    }

    return array($startdate,$enddate);
}