Why would one use function pointers to member method in C++?

Question

A lot of C++ books and tutorials explain how to do this, but I haven\'t seen one that gives a convincing reason to choose to do this.

I understand very well why functio

Answer 1

In the past, member function pointers used to be useful in scenarios like this:

class Image {
    // avoid duplicating the loop code
    void each(void(Image::* callback)(Point)) {
        for(int x = 0; x < w; x++)
            for(int y = 0; y < h; y++)
                callback(Point(x, y));
    }

    void applyGreyscale() { each(&Image::greyscalePixel); }
    void greyscalePixel(Point p) {
        Color c = pixels[p];
        pixels[p] = Color::fromHsv(0, 0, (c.r() + c.g() + c.b()) / 3);
    }

    void applyInvert() { each(&Image::invertPixel); }
    void invertPixel(Point p) {
        Color c = pixels[p];
        pixels[p] = Color::fromRgb(255 - c.r(), 255 - r.g(), 255 - r.b());
    }
};

I've seen that used in a commercial painting app. (interestingly, it's one of the few C++ problems better solved with the preprocessor).

Today, however, the only use for member function pointers is inside the implementation of boost::bind.