Trouble using callback with class member function

Question

I am having trouble compiling the following code. I am usually OK with using callback functions, but it seems that when using a member function, it has issues. Do you know what is the problem with my declaration/definition of the parameter startPlayback?

class VmapPlayer
{
        void startPlayback();
        void playAdBreak(int a, void (*callback)());
};

void VmapPlayer::playAdBreak(int a, void (*callback)())
{
    cout << a << endl;
    //callback();
}

void VmapPlayer::startPlayback()
{
    playAdBreak(5, startPlayback);     // Compile issue with "startPlayback" parameter
}

Richard · Accepted Answer · 2014-01-22 19:30:16Z

1

void (*callback)() declares callback as a function pointer, but startPlayback is not a free function, but a member function. This is one way to fix it:

class VmapPlayer
{
    void startPlayback();
    void playAdBreak(int a, void (VmapPlayer::*callback)());
};

void VmapPlayer::playAdBreak(int a, void (VmapPlayer::*callback)())
{
    cout << a << endl;
    (this->*callback)();
}

void VmapPlayer::startPlayback()
{
    playAdBreak(5, &VmapPlayer::startPlayback);
}

If you need more flexibility, and C++11 is available, you could use std::function<void()> to hold your callback, and fill it with a lambda expression, like [this](){ startPlayback(); }

answered Jan 22, 2014 at 19:30

Richard

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