Matt Fago <fago@xxxxxxxxxxxxx> writes:
> It seemingly is related to friend injection (-ffriend-injection
> eliminates the message).
>
> C.h:
> ---
> #include <iostream>
> namespace A {
> namespace B {
> class C {
> public:
> friend std::ostream & operator<< ( std::ostream &os, C &in );
> };
> }
> }
This makes the function a friend but does not actually declare the
function. That is what -ffriend-injection is about: in pre-ISO C++ a
friend declaration served as a declaration, in ISO C++ it does not.
If you want to declare the function, declare it. Don't just mention it
in a friend declaration.
Ian
