1. 编写程序完成如下功能：

　　⑴ 编写一个自己的字符串类MyString，它有一个私有的数据成员：指向字符串的指针m_data。编写该类的构造函数、拷贝构造函数和析构函数，在构造函数和拷贝构造函数中动态申请内存空间赋值给m_data。用于存储字符串。在析构函数中释放内存空间。

　　⑵ 重载运算符“+”作为类MyString的成员函数，使能完成字符串相加功能。

　　⑶ 编写main函数，测试该类及被重载的运算符。-A written procedure performs the following functions: ⑴ write a string class MyString, it has a private data member: pointers to strings m_data. Write the class constructor, copy constructor and destructor, constructor and copy constructor dynamic application memory space assigned to m_data. For storing strings. Destructor to free up memory space. ⑵ overloaded operators " +"　as a the class MyString member function, so that the complete string together. ⑶ write the main function to test the class and overloaded operators.