Question

I need to set callback, but I dont want to make it global function, I dont need it public aswell, so I’ve made it private. Wondering, is it the right way to go.

class A // button object from window library. I wont change this class
{
public:
    typedef void (*fptr)();
    void set(fptr p)
    {
        p(); // here I call private static of B
    };
};
class B // my own class
{
private:
    static void prfn() {};
public:
    B()
    {
        A a;
        a.set(prfn);
    };
};
int main(){B b;}

Answer 1

Your code is fine. It is no different from the following standard idiom:

class Foo
{
    int n;
public:
    int & the_int() { return n; }
};

It’s perfectly fine to expose private members via public functions. (It may not be good design, but it’s entirely legal.) You’re doing the same thing by using a private member as a function argument for some other, unrelated purpose. Note that it is only your own class B that accesses a private member of B.