How to pass a member function to another member function?

Question

My problem is about passing a member function from a Class A, to a member function of a Class B:

I tried something like this :

typedef void (moteurGraphique::* f)(Sprite);
f draw =&moteurGraphique::drawSprite;
defaultScene.boucle(draw);

moteurGraphique is A class, moteurGraphique::drawSprite is A member function,

defaultScene is an instance of B class, and boucle is B member function.

All that is called in a member function of A:

void moteurGraphique::drawMyThings()

I tried different ways to do it, that one seems the more logical to me, but it won't work! I got:

Run-Time Check Failure #3 - The variable 'f' is being used without being initialized.

I think I am doing something wrong, can someone explain my mistake ?

What compiler are you using which checks such things during runtime? — leemes, Oct 13 '15 at 08:47
Piece of advice: Have in mind that member functions are bound to objects. — 101010, Oct 13 '15 at 08:49
Do you mean [something like this](http://ideone.com/D3b9oX)? — leemes, Oct 13 '15 at 08:54
Yes Visual C++, I know that i can do that in other ays, like static functions, but i would like to do like that, Is that even possible ? — Fabrice Palermo, Oct 13 '15 at 08:55
@FabricePalermo yes it's possible, but you need to post an [mvce](http://stackoverflow.com/help/mcve) if you need specific help. — TartanLlama, Oct 13 '15 at 09:00

Ivan · Accepted Answer · 2015-10-13T09:47:04.910

3

C++11 way:

using Function = std::function<void (Sprite)>;

void B::boucle(Function func);
...

A a;
B b;

b.boucle(std::bind(&A::drawSprite, &a, std::placeholders::_1));

edited Oct 13 '15 at 09:47

answered Oct 13 '15 at 08:58

Ivan

2,007
11
15

That still won't work, i did the c++ normal way , Thanks a lot for trying – Fabrice Palermo Oct 14 '15 at 12:06

score 2 · Answer 2 · answered Oct 13 '15 at 08:54

Member functions need to be called on objects, so passing the function pointer alone is not enough, you also need the object to call that pointer on. You can either store that object in the class that is going to call the function, create it right before calling the function, or pass it along with the function pointer.

class Foo
{
public:
    void foo()
    {
        std::cout << "foo" << std::endl;
    } 
};

class Bar
{
public:
    void bar(Foo * obj, void(Foo::*func)(void))
    {
        (obj->*func)();
    }
};

int main()
{
    Foo f;
    Bar b;
    b.bar(&f, &Foo::foo);//output: foo
}

I think i would do like that, because i am affraid, other ways wont works. I knew that member functions are attached to executed object,but i wanted a way to dynamicly bind that, Thank you ! — Fabrice Palermo, Oct 13 '15 at 09:14

score 1 · Answer 3 · answered Oct 13 '15 at 08:50

1

Can't you make drawMyThing a static function if you don't need to instantiate A, and then do something like :

defaultScene.boucle(A.drawMyThing(mySpriteThing));

?

answered Oct 13 '15 at 08:50

Magnas

869
1
5
18

Yes, i could do that easily, but i want to stay dynamic, – Fabrice Palermo Oct 13 '15 at 08:53

How to pass a member function to another member function?

3 Answers3

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