Something

class MyWindow : public Fl_Window {
    
public:
    MyWindow(const char *title, const char *button1, const char *button2, const char *button3);
    ~MyWindow();
};

MyWindow::MyWindow(const char *title, const char *button1, const char *button2, const char *button3) :
            Fl_Window(300,100,title) {
    begin();
        new Fl_Button(5,5,90,20,button1);
        new Fl_Button(105,5,90,20,button2);
        new Fl_Button(205,5,90,20,button3);
    end();
    show();
}

MyWindow::~MyWindow() {
    
}