[ACCEPTED]-C++ template/ostream operator question-ostream

Accepted answer

Score: 11

Please look at the error, it says,

friend 4 declaration 'std::ostream& operator<<(std::ostream&, const Vector&)' declares 3 a non-template function|

That means you need to make 2 the operator<< a template function.

So in the class, you've 1 to declare it as:

template<unsigned short m> //<----note this: i.e make it template!
friend std::ostream& operator <<(std::ostream& out, const Vector<m>& v);

Then define it as,

template <unsigned short m>
std::ostream& operator<<(std::ostream& out, const Vector<m>& v) {
   out << "(" << v.coords[1] << " - " << v.coords[2] << ")";
   return out;
}

Score: 7

Just define the friend function inside the 2 class.

template <unsigned short n>
class Vector
{
public:
    std::vector<float> coords;

    Vector();
    Vector(std::vector<float> crds);
    friend std::ostream& operator <<(std::ostream& out, const Vector& v)
    {
        out << "(" << v.coords[1] << " - " << v.coords[2] << ")";
        return out;
    }
};

template <unsigned short n>
Vector<n>::Vector()
{
    coords.assign(n, 0.0);
}


int main()
{
    Vector<3> toomas;
    cout << toomas;
}

Tested: http://ideone.com/LDAR4

Or, declare the template function 1 beforehand, using a forward prototype:

template <unsigned short n>
class Vector;

template <unsigned short n>
std::ostream& operator <<(std::ostream& out, const Vector<n>& v);

template <unsigned short n>
class Vector
{
public:
    std::vector<float> coords;

    Vector();
    Vector(std::vector<float> crds);
    friend std::ostream& operator << <>(std::ostream& out, const Vector& v);
};

template <unsigned short n>
Vector<n>::Vector()
{
    coords.assign(n, 0.0);
}

template <unsigned short n>
std::ostream& operator <<(std::ostream& out, const Vector<n>& v)
{
    out << "(" << v.coords[1] << " - " << v.coords[2] << ")";
    return out;
}

Tested: http://ideone.com/8eTeq

Source: stackoverflow.com

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