获取两个时间格式相差的天数

    /**
     * 获取两个时间格式相差的天数
     * @date 2019/05/23
     * @param $start_time int 开始时间戳
     * @param $end_time int 结束时间戳
     */
    public static function getTimeDiff($start_time, $end_time = null)
    {
        if (!is_numeric($start_time)) {
           $start_time = strtotime($start_time);
        }

       if (!$end_time) {
            $end_time = time(); 
        }
        if (!is_numeric($end_time)) {
           $end_time = strtotime($end_time);
        }

        while ($start_time <= $end_time){    
            $days[] = date('Y-m-d',$start_time);    
            $start_time = strtotime('+1 day',$start_time);
        }
        return count($days);
        
    }