C++ 0x11 - std::bind and composition

Question

I want to bind member class event to consumer class function while using composition. Please correct me if description of problem is wrong, I come from C# background.

Here is the code:

#include "stdafx.h"
#include <functional>
#include <iostream>

using namespace std::placeholders;

class Observable
{
public:
    void Register(std::function<void()> Callback)
    {

    }
    std::function<void()> OnStateChanged;

    void ChangeState()
    {
        std::cout << "DevicioClient::ChangeState" << std::endl;
        OnStateChanged();
    }
};

class Observer
{
    Observable client;

    void OnStateChanged()
    {
        std::cout << "DevicioConsumer::OnStateChanged" << std::endl;
    }
public:
    void Run()
    {
    // does work
        client.OnStateChanged = []{
            std::cout << "client.OnStateChanged" << std::endl;
        };
    // doesn't work
    //  OnStateChanged = std::bind(&Observable::OnStateChanged, this);

        client.ChangeState();
    }
};
int _tmain(int argc, _TCHAR* argv[])
{
    Observer consumer;
    consumer.Run();

    getchar();
    return 0;
}

I want to run Observer::OnStateChanged when Observable call OnStateChanged function.

@АндрейБеньковский: Not to mention `#include "stdafx.h"`... — Christian Hackl, Nov 01 '15 at 10:25
@ChristianHackl "stdafx.h" has to do with [precompiled headers](http://stackoverflow.com/a/4726838/5420829) — Андрей Беньковский, Nov 01 '15 at 10:36
@АндрейБеньковский: I know. What do precompiled headers have to do with the question? — Christian Hackl, Nov 01 '15 at 10:38
If you're looking for a robust simulacrum to c# closures and automatic reference counting, you may want to bind your function to a `shared_ptr` or a lambda that strengthens a `weak_ptr` to your observer rather than simply `this`. An excellent library is of course boost::signals2, which is also thread-safe and offers complete reference counting support through the `track_foreign` member function. — Richard Hodges, Nov 01 '15 at 11:29
_tmain _TCHAR and #include "stdafx.h" were added by by visual studio when i created example console application. Should i remove them? Is visual studio wrong? — toomasz, Nov 01 '15 at 12:01

score 3 · Accepted Answer · edited Nov 01 '15 at 09:34

3

It says &Observable::OnStateChanged for the function you tried to bind... did you mean &Observer::OnStateChanged? Because this works ok:

client.OnStateChanged = std::bind(&Observer::OnStateChanged, this);

edited Nov 01 '15 at 09:34

Alan Stokes

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answered Nov 01 '15 at 09:31

ClockworkV

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C++ 0x11 - std::bind and composition

1 Answers1