Friend member function cannot access private member

Question

I have the following:

class B;

class A
{
public:
    int AFunc(const B& b);
};

class B
{
private:
    int i_;
    friend int A::AFunc(const B&);
};

int A::AFunc(const B& b) { return b.i_; }

For the definition of AFunc I get that member B::i_ is inaccessible. What am I doing wrong?

Compiler: MSVC 2013.

Update: Changed AFunc to public and the code now compiles. However I still get an IntelliSense error. Is this a problem with IntelliSense?

Answer 1

The problem is that you are were declaring another class's private function as a friend! B should normally have no knowledge of A's private member functions. G++ 4.9 has the following to say:

test.cpp:6:9: error: 'int A::AFunc(const B&)' is private
     int AFunc(const B& b);
         ^
test.cpp:13:33: error: within this context
     friend int A::AFunc(const B&);
                                 ^

To solve this, simply declare B as a friend of A:

class A
{
    friend class B;
private:
    int AFunc(const B& b);
};

You might be interested in Microsoft's example.