C++: static function wrapper that routes to member function?

Question

I\'ve tried all sorts of design approaches to solve this problem, but I just can\'t seem to get it right.

I need to expose some static functions to use as callback f

Answer 1

Something like the below. The singleton is in class Callback, the Instance member will return a statically allocated reference to a CallbackImpl class. This is a singleton because the reference will only be initialised once when the function is first called. Also, it must be a reference or a pointer otherwise the virtual function will not work.

class CallbackImplBase
{
public:
   virtual void MyCallBackImpl() = 0;
};

class CallbackImpl : public CallbackImplBase
{
public:
    void MyCallBackImpl()
    {
        std::cout << "MyCallBackImpl" << std::endl;
    }
};

class Callback
{
public:
    static CallbackImplBase & Instance()
    {
        static CallbackImpl instance;
        return instance;
    }

    static void MyCallBack()
    {
        Instance().MyCallBackImpl();
    }
};

extern "C" void MyCallBack()
{
    Callback::MyCallBack();
}