说明：  这个代码是STRING类的声明及实现,因为我认为C++类库中的string类比较庞大,找一个函数需要很长时间,所以用一个简单明了的代替之.
(STRING kind of statement and realized, because I think the C library string of relatively large, a function for a very long time. Therefore, the use of a simple and straightforward replaced it.)