assign a member function to a function pointer

Question

If I have two classes like this :

class A
{
    public:
        int *(*fun)( const int &t );
        A( int *( *f )( const int &t ) ) : fun( f ) {}
};
         


        

Answer 1

this result in compiler error

Because f is a A's non-static member function returning int*, that accepts single const reference to int. That means, that its type is not:

int* (*)(const int &);

but:

int* (A::*)(const int&);

Also, your code signalizes very bad design - I think you need simple virtual function. But if you want to keep writing things this way, you may want to read: ISOCPP: Pointers to members.

Remember, that non-static member functions of type C always accepts additional implicit argument of type C* (or const C*, if function is declared with const qualifier), that points to instance of C this function was called on.

Answer 2

Your code looks confusing and, personally, I believe that C function pointers look ugly on C++'s OO implementation. So I would advise you to use the std::function. It only has been available since C++11. If you cannot use it, try looking on Boost's Implementation.

I can give you an example of how to use the std::function:

bool MyFunction(int i)
{
    return i > 0;
}

std::function<bool(int)> funcPointer = MyFunction;

Using this you will drastically improve your code reliability. As of your problem, specifically:

class A
{
public:
    std::function<int*(const int&)> fun;
    A(std::function<int*(const int&)> f) : fun(f) {}
};

class B
{
private:
    float r;
    int *f(const int &t)
    {
        return new int(int(r) + t);
    }
    A *a;
    B()
    {

        std::function<int*(const int&)> tempFun = std::bind(&B::f, this, _1);
        a = new A(tempFun);
    }
};

You have to add the following namespace:

using namespace std::placeholders;

Answer 3

So what to do

Not much. Other than templating A on the type of objects for which it will hold a pointer to a member function taking a reference to a const int and returning a pointer to int.

What you're trying to do is to mix a pointer to a free function with a pointer to member function. Whilst it sounds like they're both function pointers they're different enough to not be able to pass through the same type definition.