error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'RatNum' (or there is no acceptable conversion)

Question

I'm having an issue with overloading the << operator. I tried to find an answer already but it seemed that most people just hadn't implemented an override. I'm just learning C++ but I believe it may be a scope issue. I am trying to print out a Rational Number (fractions and integers) class, which has two members for the numerator and denominator.

Header file:

#ifndef RATMATH_H
#define RATMATH_H

using namespace std;

class RatMath
{

public:
    RatMath(void);

    virtual ~RatMath();

    friend ostream& operator<<(ostream &output, RatNum &resultObj);

};
#endif

in the RatMath class:

ostream& operator<<(ostream &output, RatNum &resultNum)
{
    int topNum = resultNum.getTopNum();
    int botNum = resultNum.getBotNum();

    output << topNum << "/" << botNum;
    return output;
}

and then to call it from int main(), in a GUI class (which isn't declared in the header-not sure if that is an issue but it was working alright before):

RatNum testObj = RatNum(1, 3);
cout << testObj;

I tried putting the override right in the GUI class to see if it was a scope issue, but then I don't know where to put the 'friend' declaration since the GUI class isn't defined in the header. either way, it didn't work. Any ideas?

Answer 1

Your function has the wrong types:

friend ostream& operator<<(ostream &output, RatNum &resultObj);

should be:

friend ostream& operator<<(ostream &output, **const** RatNum &resultObj);

Answer 2

Your friend declaration of

friend ostream& operator<<(ostream &output, const RatNum &resultObj);

should be placed in the (header of) RatNum class, not in the (header of) RatMath Class.