overloaded >> operator problem

**quizkiwi** · 07-19-2005

I am trying to overload an the >> operator for my new Money class. It compiles fine, however when it gets to the point where i use the operator it, seems to loop the input method for a while and then end the program skipping any code after it. Any ideas?

Code:

money.h

class Money
{
    private:
        int cents;

    public:
        Money();
        Money(int cent);

        void input(istream &in) const;
};

istream & operator>> (istream & in, const Money & m);

Code:

money.cpp

Money::Money(){}

Money::Money(int cent)
{
    cents = cent;
}

void Money::input(istream &in) const
{
    //THIS IS WHERE IT LOOPS UNTIL ENDING THE PROGRAM
    in >> cents;
}

istream& operator>>(istream & in, const Money &m)
{
   m.input( in );
   return in;
}

Code:

testMoney.cpp

int main()
{
    Money m();
    cin >> m;
}

The program never allows you to enter anything from the cin >> cents command. I have more code, but i am trying to simplify it...if you need to see more, let me know.

Thanks

**mrafcho001** · 07-19-2005

Im pretty sure you are suppose to add the operator function inside the class, and it is suppose to return the class(in your case its return type is suppose to be Money)

**quizkiwi** · 07-19-2005

That would be the case if I wasn't making the input() function a member method and just passing the istream to the overloaded function. Thanks for looking

**Codeplug** · 07-19-2005

>> It compiles fine...
Not what you've posted. The input() method is const and therefore can't modify 'cents'.

>> ...but i am trying to simplify it...
Once you think you've simplified it. Compile and run it to make sure it still demonstrates the issue.

gg

**Darryl** · 07-19-2005

1st you need to make your overload a friend function.
2nd you don't need the input() AND the operator>> overload functions unless you just are trying to create dual methods for input.
3rd The Money parameter, shouldn't be a constant, because you are trying to change it with the inputted value.
4th, I added the namespace std:: but I imagine you have just omitted that you are using namespace std since you say it compiles.

Code:

class Money
{
	friend std::istream& operator>>(std::istream & in, Money &m);

    private:
        int cents;

    public:
        Money();
        Money(int cent);
};

Code:

Money::Money(){}

Money::Money(int cent)
{
    cents = cent;
}


std::istream& operator>>(std::istream & in, Money &m)
{
	int amount = 0;
	in >> amount;
	m.cents = amount;
	return in;
}

**Daved** · 07-19-2005

Your operator>> should not take a const Money reference, it should take a plain Money reference sine it will modify the variable. Also, the input member function should not be const.

In your example code you should declare a new instance of money without the parentheses (i.e. use Money m; ). The way you have it declares a function instead of a variable.

The const thing might be what's causing the problem, since it compiles but fails on the platform I tested. But if it isn't, it is likely due to other code messing up the stream state.

Darryl, just making operator>> a friend might be preferred, but there's nothing wrong with having an input function that does the work instead.

**Darryl** · 07-19-2005

Originally Posted by Daved

Darryl, just making operator>> a friend might be preferred, but there's nothing wrong with having an input function that does the work instead.

I would agree if input() was able to stand on it's own, but in this case, it appears the input() is only a work around for not using friend. Using friend is the simpler and more effiecient.

**quizkiwi** · 07-19-2005

thanks everyone, removing the const worked. I am not using a friend decleration because this is for a class and i must demonstrate that i understand what the teacher taught

. sorry codeplug for not being more thorough, and the m() was a typo, so everything compiles and runs as desired

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