c++ - 使自定义类ostream可输出？

我正在尝试从支票和储蓄帐户中打印余额。我知道您无法使用void函数返回值，但是我可以用哪种方式显示两个帐户的余额？

#ifndef ACCOUNT_H
#define ACCOUNT_H

// Account.h
// 4/8/14
// description

class Account {
private:
    double balance;
    double interest_rate; // for example, interest_rate = 6 means 6%
public:
    Account();
    Account(double);
    void deposit(double);
    bool withdraw(double); // returns true if there was enough money, otherwise false
    double query();
    void set_interest_rate(double rate);
    double get_interest_rate();
    void add_interest();
};

#endif


// Bank.cpp
// 4/12/14
// description

#include <iostream>
#include <string>
#include "Bank.h"

using namespace std;

Bank::Bank(): checking(0), savings(0) { }

Bank::Bank(double checking_amount, double savings_amount): checking(checking_amount), savings(savings_amount){;

    checking = Account(checking_amount);
    savings = Account(savings_amount);
}

void Bank::deposit(double amount, string account)
{
    if (account == "S") {
        savings.deposit(amount);
    } if (account == "C") {
        checking.deposit(amount);
    }
}

void Bank::withdraw(double amount, string account)
{
    if (account == "S") {
        savings.withdraw(amount);
    } if (account == "C") {
        checking.withdraw(amount);
    }
}

void Bank::transfer(double amount, string account)
{
    if (account == "S") {
        savings.deposit(amount);
        checking.withdraw(amount);
    } if (account == "C") {
        checking.deposit(amount);
        savings.withdraw(amount);
    }
}

void Bank::print_balances()
{
    cout << savings << endl;
    cout << checking << endl;

}

#ifndef BANK_H
#define BANK_H

// Bank.h
// 4/12/14
// description

#include <string>

#include "Account.h"

using namespace std;

class Bank {
private:
    Account checking;
    Account savings;
public:
    Bank();
    Bank(double savings_amount, double checking_amount);
    void deposit(double amount, string account);
    void withdraw(double amount, string account);
    void transfer(double amount, string account);
    void print_balances();
};

#endif

我在void Bank :: print_balances（）下遇到2个错误。它只是说：

"no match for 'operator<<' in 'std::cout << ((Bank*)this) ->Bank::savings'"

我已经阅读了很多，但是我所学到的是因为“支票”和“储蓄”是一种帐户类型，因此无法使用。我以前的项目与此类似，而我使用了“双精度”类型，因此我能够返回一个值。

抱歉，如果格式错误。首次在此网站上发布。

最佳答案

您需要为自定义类operator<<重载Account以便能够cout<<其对象。

class Account {
    ...
public:
    friend ostream& operator<<(ostream &os, const Account &dt);
    ...
};

ostream& operator<<(ostream &os, const Account &dt)
{
    os << dt.balance; // print its balance
    return os;
}

要继续阅读，请签出Overloading the I/O operators。