Pass an objects member function as argument (function pointer)

Question

I have a pointer to an object 'eventHandler' which has a member function 'HandleButtonEvents':

I call it like this:

eventHandler->HandleButtonEvents();

Now I want to pass a pointer to the member-function 'HandleButtonEvents()' of the class 'EventHandler' as an argument to another the object 'obj' like in this Stackoverflow example:

ClassXY obj = ClassXY(eventHandler->HandleButtonEvents);

The constructor is declared like this:

ClassXY(void(*f)(void));

The compiler tells me:

error : invalid use of non-static member function

What am I doing wrong?

Pointers to non-static member functions are not the same as a pointer to a non-member function. I recommend you look into [`std::function`](http://en.cppreference.com/w/cpp/utility/functional/function) and [`std::bind`](http://en.cppreference.com/w/cpp/utility/functional/bind) instead. — Some programmer dude, Nov 03 '16 at 12:00
@skypjack: can't use that because I can't include the type in that class (include-loop). That's why I try to use the function pointer... — C.P., Nov 03 '16 at 12:06
@C.P. Well, a pointer to function and a pointer to member function are really different beasts. — skypjack, Nov 03 '16 at 12:08
@skypjack: Ok. I changed the question. I need a pointer to a member function (of another object) — C.P., Nov 03 '16 at 12:09
@C.P. In order for a pointer-to-member to be usable, C++ has to know what it's a member of. If you can't actually provide that then you'll need to make your class and/or its constructor `template`'d. — Olipro, Nov 03 '16 at 12:19

score 1 · Answer 1 · answered Nov 03 '16 at 12:29

Using std::function and std::bind as suggested in my comment makes it very easy:

#include <iostream>
#include <functional>

class ClassXY
{
    std::function<void()> function;

public:
    ClassXY(std::function<void()> f)
        : function(f)
    {}

    void call()
    {
        function();  // Calls the function
    }
};

class Handler
{
public:
    void HandleButtonEvent()
    {
        std::cout << "Handler::HandleButtonEvent\n";
    }
};

int main()
{
    Handler* handler = new Handler;

    ClassXY xy(std::bind(&Handler::HandleButtonEvent, handler));

    xy.call();
}

See here for a live example.

Pass an objects member function as argument (function pointer)

1 Answers1

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