CODEWITHSUNDEEP
c++callback
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code

Reputation: 5642

Trouble using callback with class member function

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
}

Upvotes: 0

Views: 86

Answers (1)

Richard
Richard

Reputation: 212

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(); }

Upvotes: 1

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