该函数不仅可求出某个时间前(后)一段时长的日期与时间，而且可得出这个日期是星期几,给程序设计带来不少便利，也方便了费用的计算与核实，读者可直接调用该函数。 -This function can be derived not only some time ago (after) a long time the date and time, but can come to this date is a few weeks to bring a lot of procedures to facil