php前几天开始算起往后几天的日期计算

    /*
    *参数 param day  近几天
*参数 param size  间隔几天
*/
public function card_list(){

  $day=$this->request->param('day',1);
  $size=$this->request->param('size',1);
  #时间计算
  $start_time =strtotime('-'.$day.' day');
  $current_date =date('Y-m-d',$start_time);
  $current_m=date('m',$start_time);
  $current_d=date('d',$start_time);
  $current_Y=date('Y',$start_time);

  $start_date =$current_date.' 00:00:01';
  $end_date = date('Y-m-d H:i:s',mktime(0,0,0,$current_m,$current_d+$size,$current_Y)-1);
  echo $start_date;
  echo '<br>';
  echo $end_date;
}