通过多种成员函数的定义和运算符的重载，实现字符串的各种直接操作。比如：去掉串首、串尾与子串相同的字符，子串在主串中的定位，用新子串更换主串中的指定子串，比较字符串的大小，字符串连接等-Through a variety of member function definitions and operator overloading to achieve a variety of direct manipulation of the string. For example: remove the string head, tail and string substring same character string substring in the main location, with a new sub-string replacement of the main stream of the specified substring, compare the size of the string, the string connections