总结：

1、等号操作符重载注意事项：
    （1）防止自身赋值
    （2）先将自身的额外开辟的空间回收掉
    （3）执行深拷贝
2、注意函数的返回引用或者元素：如果需要连续使用 返回元素
3、如果一个函数传递const修饰的对象，那么此对象调用的成员函数也应为const类型
4、重载小括号 称这种对象为仿函数
5、字符串>>重载时防止初始化的字符串长度为空

MyString.h:
 

#pragma once
#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
using namespace std;
class MyString
{
public:MyString();MyString(int len); //创建一个长度为len的string对象MyString(const char*str);MyString(const MyString& another);~MyString();//重载操作符[]  //char* operator[](int index);char& operator[](int index);  //mystring.operator[](index)//重载操作符<<  friend ostream& operator<<(ostream& os, MyString &mystring);//重载操作符>>friend istream& operator>>(istream& is, MyString &mystring);  //重载操作符==bool operator==(const MyString &mytring2) ;//重载操作符!=friend bool operator!=(MyString &mystring1, MyString &mytring2);//重载操作符=//MyString operator=(const MyString &another);MyString& operator=(const MyString &another);//重载操作符+ 可以连加 所以返回匿名对象 不加引用//如果加引用 第一次加法后返回一个乱码值//friend MyString& operator+(const MyString &another1, const MyString &another2);MyString operator+(MyString &another);private:int len;char *str;
};

MyString.cpp:

#include "MyString.h"MyString::MyString()
{this->len = 0;this->str = NULL; //表示零值或空值//this->str = "";  //表示空字符串 里面有\0
}MyString::MyString(int len)
{this->len = len;this->str = new char[len];
}MyString::MyString(const char * str)
{/*meint len = strlen(str);this->len = len + 1;this->str = new char[len + 1];for (int i = 0; i < len; i++){this->str[i] = str[i];}*/if (str == NULL) {this->len = 0;this->str = new char[0+1]; strcpy(this->str, "");}else {int len = strlen(str);this->len = len;this->str = new char[len + 1];strcpy(this->str, str);}
}MyString::MyString(const MyString & another)
{//拷贝构造函数不需要回收垃圾 初始化时被调用this->len = another.len;this->str = new char[this->len + 1];strcpy(this->str, another.str);}MyString::~MyString()
{if (this->str != NULL) {cout << this->str << "执行了析构函数" << endl;delete [] this->str;this->str = NULL;this->len = 0;}
}char& MyString::operator[](int index)
{// TODO: 在此处插入 return 语句return this->str[index];
}bool MyString::operator==(const MyString & mystring2)
{if (this->len != mystring2.len) {return false;}for (int i = 0; i < this->len; i++){if (this->str[i] != mystring2.str[i]) {return false;}}return true;
}MyString& MyString::operator=(const MyString & another)
{if (this == &another) {return *this;}// TODO: 在此处插入 return 语句if (this->str != NULL) {delete this->str;this->str = NULL;this->len = 0;}this->len = another.len;this->str = new char[this->len + 1];strcpy(this->str, another.str);return *this;}ostream& operator<<(ostream& os, MyString &mystring) {cout << "len:";os << mystring.len;cout << "str:";os<< mystring.str ;return os;
}istream& operator>>(istream &is, MyString &mystring)
{// TODO: 在此处插入 return 语句//先释放mystring内存//char *str=NULL;cin>>str; 程序崩溃//1、将mystring之前的字符串释放掉if (mystring.str != NULL) {delete mystring.str;mystring.str = NULL;mystring.len = 0;}//2、通过cin添加新的字符串char temp_str[4096] = { 0 };cin >> temp_str;int len = strlen(temp_str);mystring.str = new char[len + 1];strcpy(mystring.str, temp_str);mystring.len = len;return is;
}MyString MyString::operator+(MyString & another)
{// TODO: 在此处插入 return 语句MyString temp;int len= this->len + another.len;temp.len = len;temp.str = new char[len + 1];memset(temp.str, 0, len + 1);  //清空 strcat需要memset  strcpy不需要strcat(temp.str, this->str);strcat(temp.str, another.str);//temp.str = this->str + another.str;return temp;
}
bool operator!=(MyString &mystring1,MyString &mytring2) {return !(mystring1 == mytring2);
}

main.cpp:

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<string>
#include"MyString.h"
using namespace std;void test01() {string s1("123");//equal tostring s2 = "123";string s3(s1);  //重载拷贝构造string s4;  s4 = s1;       //重载=s4 = s1 + s2;  //重载+s2[1] = 'x';   //重载[]cout << s2 << endl;  //重载<<
}
/*
1x3
*/void test02() {MyString s1;MyString s2("123");//MyString s3(NULL);MyString s4(s2);//cout <<"s1"<< s1 << endl;  截断后面输出cout << "s2" << s2 << endl;cout << "s4" << s4 << endl;s2[1] = 'x';cout << "s2" << s2 << endl;cout << "s4" << s4 << endl;MyString s5;s5 = s2;cout << "s5" << s5 << endl;
}
/*
s2len:3str:123
s4len:3str:123
s2len:3str:1x3
s4len:3str:123
s5len:3str:1x3
1x3执行了析构函数
123执行了析构函数
1x3执行了析构函数
*/
void test03() {MyString s1("abc");cin >> s1;cout << s1 << endl;
}
/*
ddd
len:3str:ddd
ddd执行了析构函数
*/
void test04() {
#if 0string s1("123");string s2("456");cout << (s1 + s2)+s2 << endl;cout << s1 << endl;cout << s2 << endl;
#endifMyString s1("123");MyString s2("456");cout << (s1 + s2) << endl;cout << s1 << endl;cout << s2 << endl;
}
/*
123456执行了析构函数
len:6str:123456
123456执行了析构函数
len:3str:123
len:3str:456
456执行了析构函数
123执行了析构函数
*/
void test05() {
#if 0string s1("123");string s2("456");if (s1 == s2) {cout << "等于" << endl;}elsecout << "不等于"<< endl;
#endif //等价于MyString s1("123");MyString s2("456");if (s1 == s2) {cout << "等于" << endl;}elsecout << "不等于" << endl;if (s1 != s2) {cout << "bu等于" << endl;}elsecout << "等于" << endl;
}
/*
不等于
bu等于
456执行了析构函数
123执行了析构函数
*/
int main() {test01();//test02();//test03();//test04();//test05();return 0;
}