设计一个字符串类MYMYMYSTRING，具有构造 * * 函数、析构函数、拷贝构造函数等， * * 尽可能的完善它，使之能满足各种需要-Designing a string class MYMYMYSTRING, with a constructor* function, destructor, copy constructor, etc.** It is perfect as far as possible, so that it can meet the various nee