Making a custom class ostream outputable?

Question

I'm trying to print the balance from a checking and savings account. I know you can't return a value using the void function, but in what way can I show the balances for both accounts?

#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

I'm getting 2 errors under void Bank::print_balances(). It just says:

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

I was reading a lot about it, but all I learned was since "checking" and "savings" are an account type, it won't work. My previous project similar, and I had "double" types instead so I was able to return a value.

Sorry if the format is wrong. First time posting on this site.

If you want to output an `Account`, you have to [overload](http://stackoverflow.com/questions/4421706/operator-overloading) the operator to tell it how. — chris, Apr 14 '14 at 15:18
How is the question related to the title? Other than that, you should put a bit more effort into simplifying the question. There is a lot of code there that is clearly unrelated (like the implementation of all other member functions in both `Bank` and `Account`), the `Bank` member definitions are provided *before* the declarations forcing others to scan back and forth in the code... — David Rodríguez - dribeas, Apr 14 '14 at 15:19
Related question: http://stackoverflow.com/questions/10291385/overloading-operator-for-stdostream — CppChris, Apr 14 '14 at 15:21

herohuyongtao · Answer 1 · 2014-04-14T15:48:39.463

3

You need to overload operator<< for your custom class Account in order to be able to cout<< its objects.

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;
}

To read on, check out Overloading the I/O operators.

edited Apr 14 '14 at 15:48

answered Apr 14 '14 at 15:24

herohuyongtao

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score 2 · Answer 2 · answered Apr 14 '14 at 15:20

2

Check this page: Overloading the << Operator for your own class. It illustrates how you can get cout to print your class in exactly the way you want.

answered Apr 14 '14 at 15:20

Lee White

3,649
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Ivan Aksamentov - Drop · Answer 3 · 2014-04-14T16:01:21.287

You do not returning anything in Bank::print_balances() (and you can not, because it is a void function)
What you doing now is passing savings and checking (both of type Account) to std::cout as arguments of operator<<()
The problem is that, by default, std::cout "knows" how to output only primitive types (such as int, float, double etc.) and some C++ standard library types (such as std::string).

So, you have two options:

either output primitive types obtained from Account objects via getters:

class Account {
      ...
      double GetBalance() const { return balance; }
      ...
};

void Bank::print_balances()
{
     std::cout << savings.GetBalance();
     ...

or tell std::cout how to print Account objects, by overloading operator<<() (as described in other answers).

std::ostream& operator<<(std::ostream& os, const Account& a)
{
    os << a.GetBalance();
    return os;
}

You would never want to store money amounts in floating point variable! (only if you don't agree to loose some coins every time you making sum or multiply)

I'd rather do the 2nd option since Account.h and Bank.h cannot be modified any further. But what you said, does that mean I have to put the ostream code in Account.h within the class brackets? When I put it in my Bank.cpp file (the one with the initial error), it said my checkings and savings accounts were private (and I can't change that). Thank you — , Apr 14 '14 at 15:50
@user3532512 Usually we make `operator<<()` as free function. That means you put declaration in `Account.h` and definition in `Account .cpp`. But you can put it virtually anywhere. Still you must have possibility to get a value of `balance` which is `private` member. — Ivan Aksamentov - Drop, Apr 14 '14 at 15:58

score 1 · Answer 4 · answered Apr 14 '14 at 15:25

1

you don't have overloaded "<<" operator in your Account class. compiler doesn't know how and what to cout, you should overload insertion operator of Account class.

answered Apr 14 '14 at 15:25

Bramsh

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Making a custom class ostream outputable?

4 Answers4