本字符串类可以直接用 , =,[],==操作符,并可在需要时直接转化为char*类型,程序把cpy(char*)及cat(char*)函数放在protected节中,方便在扩展本类时,进行继承并简化使用-The string class can be used directly++ =, [], the == operator, and may need to translate directly into char* type, the program cpy (char*) and cat