Add simple gtkmm3 code

src/main.cpp

@@ -1,19 +1,50 @@
-#include <gtk/gtk.h>
+#include <gtkmm.h>
+#include <iostream>
 
-void end_program(GtkWidget *wid, gpointer ptr)
+class CloseButton : public Gtk::Button
 {
-    gtk_main_quit();
+private:
+  void on_button_clicked();
+  Glib::RefPtr<Gtk::Application> app;
+public:
+  CloseButton(const Glib::ustring &label, Glib::RefPtr<Gtk::Application> app);
+};
+
+CloseButton::CloseButton(const Glib::ustring &label, Glib::RefPtr<Gtk::Application> app)
+{
+  this->app = app;
+
+  set_label(label);
+
+  signal_clicked().connect(sigc::mem_fun(*this, &CloseButton::on_button_clicked));
+
+}
+
+void CloseButton::on_button_clicked()
+{
+  this->app.get()->quit();
+}
+
+class MyWindow : public Gtk::Window
+{
+public:
+  MyWindow();
+};
+
+MyWindow::MyWindow()
+{
+  set_title("Basic application");
+  set_default_size(200, 200);
 }
 
 int main(int argc, char* argv[])
 {
-    gtk_init(&argc, &argv);
-    GtkWidget *win = gtk_window_new(GTK_WINDOW_TOPLEVEL);
-    GtkWidget *btn = gtk_button_new_with_label("Close Window");
-    g_signal_connect(btn, "clicked", G_CALLBACK(end_program), NULL);
-    g_signal_connect(win, "delete_event", G_CALLBACK(end_program), NULL);
-    gtk_container_add(GTK_CONTAINER(win), btn);
-    gtk_widget_show_all(win);
-    gtk_main();
-    return 0;
+  auto app = Gtk::Application::create("org.gtkmm.examples.base");
+  MyWindow window;
+
+  CloseButton button("Close", app);
+  window.add(button);
+  window.show_all();
+
+  return app->run(window);
 }