Linking error with friend function in template class

Question

I have a linking problem when using a home-made Complex class.

Class definition:

template
class Complex
{
public:
    Complex(const T real         


        

Answer 1

The function declared as

template <typename T>
class Complex {
    // ...
    friend T abs(Complex<T>& z);
    // ...
};

is not a function template! It looks a bit like one as it is nested within a class template but that isn't quite enough. Here is what you probably meant to write:

template <typename T> class Complex;
template <typename T> T abs(Complex<T>&);


template <typename T>
class Complex {
    // ...
    friend T abs<T>(Complex<T>& z);
    // ...
};

Alternatively, you could implement abs() when declaring it as friend.