FLTK callback with classes

test.cpp

/*
Compiling

Windows:
g++ test.cpp -o test -std=gnu++11 -lfltk -lfltk_images -lole32 -luuid -lcomctl32 -lwsock32 -lgdi32 -lcomdlg32
*/
#include <FL/Fl.H>
#include <FL/Fl_Window.H>
#include <FL/Fl_Button.H>

#include <iostream>

class MyClass
{
private:
    Fl_Window *win;
    int i;

public:
    MyClass()
    {
        i = 1;
        win = new Fl_Window(90, 100);

        Fl_Button *button = new Fl_Button(10, 10, 70, 20, "Button 1");
        button->callback([] (Fl_Widget*, void* data) {
            (static_cast<MyClass*> (data))->handleButtonClick("Button 1"); }, this);

        button = new Fl_Button(10, 40, 70, 20, "Button 2");
        button->callback([] (Fl_Widget*, void* data) {
            (static_cast<MyClass*> (data))->handleButtonClick("Button 2"); }, this);
    }
    
    void show()
    {
        win->show();
    }

    void handleButtonClick(const char *msg)
    {
        std::cout << msg << " - " << i++ << std::endl;
    }
};

int main() {
     MyClass myClass;
     myClass.show();
     return(Fl::run());
}