c++ - 使自定义类 ostream 可输出？

Question

我正在尝试打印支票和储蓄账户的余额。我知道您不能使用 void 函数返回值，但我可以用什么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() 下收到 2 个错误。它只是说:

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

我阅读了很多有关它的内容，但我所了解到的只是因为“支票”和“储蓄”是一种帐户类型，所以它不起作用。我之前的项目与此类似，但我使用的是“双”类型，所以我能够返回一个值。

如果格式有误请见谅。第一次在这个网站上发帖。

Answer 1

你需要重载 operator<<为您的自定义类(class) Account为了能够cout<<它的对象。

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，请查看 Overloading the I/O operators .