class Complex{
public:
    Complex(int flag){
        this->flag = flag;
    }
    Complex& operator+=(Complex& complex){
        this->flag = this->flag + complex.flag;
        return *this;
    }
    bool operator&&(Complex& complex){
        return this->flag && complex.flag;
    }
public:
    int flag;
};
int main(){
    Complex complex1(0); //flag 0 
    Complex complex2(1); //flag 1
    //原来情况，应该从左往右运算，左边为假，则退出运算，结果为假
    //这边却是，先运算（complex1+complex2），导致，complex1 的 flag 变为
    complex1+complex2 的值， complex1.a = 1
    // 1 && 1
    //complex1.operator&&(complex1.operator+=(complex2))
    if (complex1 && (complex1 += complex2)){ 
         //complex1.operator+=(complex2)
        cout << "真!" << endl;
    }
    else{
        cout << "假!" << endl;
    }
    return EXIT_SUCCESS;
}

        根据内置&& 的执行顺序，我们发现这个案例中执行顺序并不是从左向右，而是先 右猴左，这就是不满足我们习惯的特性了。由于 complex1 += complex2 先执行， 导致 complex1 本身发生了变化，初始值是 0 ，现在经过 += 运算变成 1,1 && 1 输出 了真。

=, [], () 和 -> 操作符只能通过成员函数进行重载

<< 和 >> 只能通过全局函数配合友元函数进行重载

不要重载 && 和 || 操作符，因为无法实现短路规则

常规建议

字符串类封装

MyString.h

#define _CRT_SECURE_NO_WARNINGS
#pragma once
#include <iostream>
using namespace std;
class MyString
{
    friend ostream& operator<< (ostream & out, MyString& str);
    friend istream& operator>>(istream& in, MyString& str);
public:
    MyString(const char *);
    MyString(const MyString&);
    ~MyString();
    char& operator[](int index); //[]重载
    //=号重载
    MyString& operator=(const char * str);
    MyString& operator=(const MyString& str); 
    //字符串拼接 重载+号
    MyString operator+(const char * str );
    MyString operator+(const MyString& str);
    //字符串比较
    bool operator== (const char * str);
    bool operator== (const MyString& str);
private:
    char * pString; //指向堆区空间
    int m_Size; //字符串长度 不算'\0'
};

MyString.cpp

#include "MyString.h"
//左移运算符
ostream& operator<< (ostream & out, MyString& str)
{
    out << str.pString;
    return out;
}
//右移运算符
istream& operator>>(istream& in, MyString& str)
{
    //先将原有的数据释放
    if (str.pString != NULL)
    {
        delete[] str.pString;
        str.pString = NULL;
    }
    char buf[1024]; //开辟临时的字符数组，保存用户输入内容
    in >> buf;
    str.pString = new char[strlen(buf) + 1];
    strcpy(str.pString, buf);
    str.m_Size = strlen(buf);
    return in;
}
//构造函数
MyString::MyString(const char * str)
{
    this->pString = new char[strlen(str) + 1];
    strcpy(this->pString, str);
    this->m_Size = strlen(str);
}
//拷贝构造
MyString::MyString(const MyString& str)
{
    this->pString = new char[strlen(str.pString) + 1];
    strcpy(this->pString, str.pString);
    this->m_Size = str.m_Size;
}
//析构函数
MyString::~MyString()
{
    if (this->pString!=NULL)
    {
        delete[]this->pString;
        this->pString = NULL;
    }
}
char& MyString::operator[](int index)
{
    return this->pString[index];
}
MyString& MyString::operator=(const char * str)
{
    if (this->pString != NULL){
        delete[] this->pString;
        this->pString = NULL;
    }
    this->pString = new char[strlen(str) + 1];
    strcpy(this->pString, str);
    this->m_Size = strlen(str);
    return *this;
}
MyString& MyString::operator=(const MyString& str)
{
    if (this->pString != NULL){
        delete[] this->pString;
        this->pString = NULL;
    }
    this->pString = new char[strlen(str.pString) + 1];
    strcpy(this->pString, str.pString);
    this->m_Size = str.m_Size;
    return *this;
}
MyString MyString::operator+(const char * str)
{
    int newsize = this->m_Size + strlen(str) + 1;
    char *temp = new char[newsize];
    memset(temp, 0, newsize);
    strcat(temp, this->pString);
    strcat(temp, str);
    MyString newstring(temp);
    delete[] temp;
    return newstring;
}
MyString MyString::operator+(const MyString& str)
{
    int newsize = this->m_Size + str.m_Size + 1;
    char *temp = new char[newsize];
    memset(temp, 0, newsize);
    strcat(temp, this->pString);
    strcat(temp, str.pString);
    MyString newstring(temp);
    delete[] temp;
    return newstring;
}
bool MyString::operator==(const char * str)
{
    if (strcmp(this->pString, str) == 0 && strlen(str) == this->m_Size){
        return true;
    }
    return false;
}
bool MyString::operator==(const MyString& str)
{
    if (strcmp(this->pString, str.pString) == 0 && str.m_Size == this->m_Size){
        return true;
    }
    return false;
}

TestMyString.cpp

void test01()
{
    MyString str("hello World");
    cout << str << endl;
    //cout << "请输入 MyString 类型字符串：" << endl;
    //cin >> str;
    //cout << "字符串为： " << str << endl;
    //测试[]
    cout << "MyString 的第一个字符为：" << str[0] << endl;
    //测试 =
    MyString str2 = "^_^";
    MyString str3 = "";
    str3 = "aaaa";
    str3 = str2;
    cout << "str2 = " << str2 << endl;
    cout << "str3 = " << str3 << endl;
    //测试 +
    MyString str4 = "我爱";
    MyString str5 = "北京";
    MyString str6 = str4 + str5;
    MyString str7 = str6 + "天安门";
    cout << str7 << endl;
    //测试 == 
    if (str6 == str7)
    {
        cout << "s6 与 s7 相等" << endl;
    }
    else
    {
        cout << "s6 与 s7 不相等" << endl;
    }
}