php日期函数例子：获取当月最后一天

/**
*  日期-获取当月最后一天
*  @return int
*/
public function get_lastday() {
  if($this->month==2) {
      $lastday = $this->is_leapyear($this->year) ? 29 : 28;
   } elseif($this->month==4 || $this->month==6 || $this->month==9 || $this->month==11) {
      $lastday = 30;
   } else {
      $lastday = 31;
   }
   return $lastday;
}

/**
*  php日期-是否是闰年
*  @return int
*/
public function is_leapyear($year) {
   return date('L', $year);
}

例子，php 日期函数之计算2个日期的差值

/**
*  php日期-计算2个日期的差值
*  @return int
*/
public function get_difference($date, $new_date) {
   $date = strtotime($date);
   $new_date = strtotime($new_date);
   return abs(ceil(($date - $new_date)/86400));
}