题目描述：
编码实现字符串类CNString，该类有默认构造函数、类的拷贝函数、类的析构函数及运算符重载，需实现以下“=”运算符、“+”运算、“[]”运算符、“<”运算符及“>”运算符及“==”运算符（备注：可以用strcpy_s, strcat_s，但禁用STL及String类），以下为各个运算符的运算效果的详细说明

“CNString.h”

#define _CRT_SECURE_NO_WARNINGS
#ifndef CNSTRING_H
#define CNSTRING_H
class CNString
{public:CNString();                                        //默认构造函数CNString(const char *Str);                         //构造函数CNString(const CNString &string);                  //拷贝构造函数~CNString();                                       //析构函数CNString & operator = (const CNString &string);    //'='运算符重载CNString  operator +(const CNString &string);      //‘+’运算符重载char & operator [](int n);                         //'[]'运算符重载bool operator < (const CNString &string);          //'<'运算符重载bool operator > (const CNString &string);          //'>'运算符重载bool operator == (const CNString &string);         //'=='运算符重载void show();                                       //输出函数private:char *str;
};
#endif

"CNString.cpp"

#include "pch.h"
#include "CNString.h"
#include<string.h>
#include<iostream>//默认构造函数
CNString::CNString()
{str = new char[1];str = '\0';
}//构造函数
CNString::CNString(const char *Str) {int len = strlen(Str) + 1;str = new char[len];strcpy(str, Str);
}//拷贝构造函数
CNString::CNString(const CNString &string) {int len = strlen(string.str) + 1;str = new char[len];strcpy(str, string.str);
}// 析构函数
CNString::~CNString()
{delete[]str;
}//'='运算符重载
CNString & CNString::operator=(const CNString &string) {int len = strlen(string.str) + 1;str = new char[len];strcpy(str, string.str);return *this;
}//‘+’运算符重载
CNString CNString::operator +(const CNString &string) {strcat(str, string.str);return *this;
}//'[]'运算符重载
char & CNString::operator [](int n) {return str[n];
}//'<'运算符重载
bool CNString::operator < (const CNString &string) {if (strcmp(str, string.str) <0)return true;elsereturn false;
}//'>'运算符重载
bool CNString::operator > (const CNString &string) {if (strcmp(str, string.str) > 0)return true;elsereturn false;
}//'=='运算符重载
bool CNString::operator == (const CNString &string) {if (strcmp(str, string.str) == 0)return true;elsereturn false;
}//输出函数
void CNString::show() {std::cout << str << std::endl;
}

"main.cpp"

// main.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//#include "pch.h"
#include"CNString.h"
#include <iostream>int main()
{   CNString CNStringstr1("abc ");CNString str2;str2 = CNStringstr1;std::cout << "'='号运算符重载测试str2=CNStringstr1："<<std::endl;std::cout << "str2=";str2.show();std::cout<<std::endl;CNString CNStringstr2("abc");CNString CNStringstr3("def ");CNStringstr2 = CNStringstr2 + CNStringstr3;std::cout << "'+'号运算符重载测试CNStringstr2 = CNStringstr2 + CNStringstr3:" << std::endl;std::cout<<"CNStringstr2 = ";CNStringstr2.show();std::cout << std::endl;CNString nstring1("abc");std::cout << "'[]'运算符重载测试：" << std::endl;std::cout<<"nstring1[0] = " << nstring1[0] << " nsting1[2] = " << nstring1[2] << std::endl;std::cout<< std::endl;CNString CNStringstr4("abc");CNString CNStringstr5("efg");std::cout << "'<'运算符重载测试："<<std::endl;if (CNStringstr4 < CNStringstr5)std::cout << "CNStringstr4 < CNStringstr5" << std::endl;std::cout << std::endl;std::cout << "'>'运算符重载测试：" << std::endl;if (CNStringstr5 > CNStringstr4)std::cout << "CNStringstr5 > CNStringstr4" << std::endl;std::cout << std::endl;CNString CNStringstr6("efg");std::cout << "'=='运算符重载测试：" << std::endl;if (CNStringstr5 == CNStringstr6)std::cout << "CNStringstr5 == CNStringstr6" << std::endl;return 0;
}

运行结果：