Is there a C++/OOP alternative to callback functions?

[knn9]

I wrote a class that represents a gui window. When an event occurs in the window, like mouse input, what is the C++ way of notifying code outside the class of the event? Currently I use function pointers, which I understand now is the C way of doing it.

[Aceix]

I think it actually depends on the API you are using. Qt uses slots and signals whith is more C++-like.

Aceix.

[knn9]

Well I use the WINAPI directly so there are no slots and signals, just the window procedures. I want to implement an event system without relying on other libraries.

[z05DSL3A]

Observer pattern?
http://en.wikipedia.org/wiki/Observer_pattern

[Cubbi]

boost has signals and slots too: http://www.boost.org/doc/libs/release/doc/html/signals2.html

[andywestken]

Well, if you're wanting to go it alone, you could possibly switch from callback functions to callback interface (or "interface") classes? (see "example" below...) But that doesn't address how you hook-up and route the events. That might lead you to implement your own version of signals and slots, I guess.

And delegates are also something to consider; the version that started off life as Boost.Function and made it into TR1 is now part of C++11, as std::function.
http://en.cppreference.com/w/cpp/utility/functional/function
(couldn't spot a cplusplus.com ref?) And there is quite a bit of forum (etc) chatter about fast C++ delegates, e.g.

Lightweight Generic C++ Callbacks (or, Yet Another Delegate Implementation)
http://www.codeproject.com/Articles/136799/Lightweight-Generic-C-Callbacks-or-Yet-Another-Del

Andy

#include <iostream>
using namespace std;

class IExample {
public:
    virtual void OnTest() = 0;
};

class Foo {
private:
    IExample* m_pCallback;

public:
    Foo() : m_pCallback(0) {
    }

    void SetCallback(IExample* pCallback) {
        m_pCallback = pCallback;
    }

    void Test() {
        if(m_pCallback) {
            m_pCallback->OnTest();
        }
    }
};

class Bar : public IExample {
public:
    /*virtual*/ void OnTest() {
        cout << "Hello world!" << endl;
    }
};

int main() {
    Foo foo;
    Bar bar;

    foo.SetCallback(&bar);
    foo.Test();
    foo.SetCallback(0);

    return 0;
}