问题重载运算符 c++

Question

我不断收到以下错误

错误（主动）E0349 没有运算符“<<”匹配这些操作数错误 C2678 二进制“<<”：未找到采用 'std::ostream' 类型左操作数的运算符（或没有可接受的转换）

我知道问题是当我尝试使运算符超载时出现错误或丢失，我认为此时它有点小，但我不知道了。任何帮助将不胜感激。

.h 文件

#include <iostream>
#include <string>
#include <ostream>

using namespace std;

#ifndef ACCOUNT_H
#define ACCOUNT_H

class account {

private:
    int acct_ID;
    string acct_name;
    float acct_balance;
    static int next_id;

public:
    account();
    account(account& rhs);
    ~account();
    account(int acct_ID, string acct_name, float acct_balance);
    void set_ID(int acct_ID);
    int get_ID()const;
    void set_name(string acct_name);
    void input();
    void set_balance(float acct_balance);
    ostream& display(ostream& stream);
    

};
ostream& operator<<(ostream& stream, account& Account); //!!!!!!!!!!!!!!!!!!!

#endif

.cpp 文件

#include "Account.h"

account::account(): acct_ID{0},acct_name{0},acct_balance{ 0 }{}

account::account(account& rhs): acct_ID{ rhs.acct_ID }, acct_name{ rhs.acct_name }, acct_balance{ rhs.acct_balance }{}

account::account(int ID, string name, float balance) :acct_ID{ ID }, acct_name{ name }, acct_balance{ balance } {


}

int account::next_id = 0;

account::~account() {}
void account::set_ID(int ID) {
    acct_ID = ID;
}

int account::get_ID()const {
    int acct_ID = 0;
    return acct_ID;
}

void account::set_name(string name) {
    acct_name = name;
}
void account::input() {
    
    cout << "Enter the name: ";
    cin >> acct_name;
    float x;
    cout << "Enter the balance: ";
    cin >> x;
    acct_balance += x;
    acct_ID = next_id;
    next_id++;
    
}
//!!!!!!!!!!!!!!!!!!!!!!!
ostream& account::display(ostream& stream) {
    stream << "Account name: " << this->acct_name;
    stream << "Account balance: " << this->acct_balance;
    stream << "Account ID: " << this->acct_ID;
    return stream;
}
ostream& operator<<(ostream& stream,account& Account) {
    stream << Account.display(stream);
    return stream;
} //!!!!!!!!!!!!!!!


void account::set_balance(float balance)
{
    acct_balance = balance;
}

Answer 1

问题是你用过：

stream << Account.display(stream);

内部超载 operator<<。这是一个问题，因为 account::display returns 一个 std::ostream 并且没有 operator<< 的重载将 std::ostream 作为参数。

方法一

要解决这个你可以为class里面的重载operator<<添加一个朋友声明和将 operator<< 的实现更改为如下所示：

class account
{
    //other members as before
   
   //friend declaration for overloaded operator<<
   friend std::ostream& operator<<(std::ostream& stream, account& Account);
};

//implementation of operator<<
std::ostream& operator<<(std::ostream& stream,account& Account) {
    stream << Account.acct_ID<<" "<< Account.acct_name<<" "<<Account.acct_balance<<" "<<Account.acct_ID;
    return stream;
}

Working demo

方法二

解决此问题的另一种方法是将 stream << Account.display(stream); 替换为 return Account.display(stream);，如下所示：

std::ostream& operator<<(std::ostream& stream,account& Account) {
    return  Account.display(stream); //changed this
}

Demo

问题重载运算符 c++

Issue overloading the operator c++

c++

operator-overloading

方法一

方法二