php计算到指定日期还有多少天的方法

function countdays($d){ $olddate = substr($d, 4); $newdate = date(Y) ."".$olddate; $nextyear = date(Y)+1 ."".$olddate;  if($newdate > date("Y-m-d"))  {  $start_ts = strtotime($newdate);  $end_ts = strtotime(date("Y-m-d"));  $diff = $end_ts - $start_ts;  $n = round($diff / 86400);  $return = substr($n, 1);  return $return;  }  else  {  $start_ts = strtotime($nextyear);  $end_ts = strtotime(date("Y-m-d"));  $diff = $end_ts - $start_ts;  $n = round($diff / 86400);  $return = substr($n, 1);  return $return;  }}