1．　　设置日期并判断日期的存在与否。2．　　减少一天和若干天。3．　　输出当前设置日期及变动以后期。4．　　保存日期至磁盘并读出。-1. Set date and the date of judgment of the existence or otherwise. 2. Reduce the day and several days. 3. Output current settings and change the date after the period. 4. Dates to disk and read.