#include <gtk/gtk.h>

static void print (GtkWidget *widget, gpointer   data) {g_print (data);}

static void activate (GtkApplication *app, gpointer user_data) {
  GtkWidget *window;
  GtkWidget *button;
  GtkWidget *box;
/*  GtkBox       GtkGrid     GtkRevealer    GtkStack
 *  GtkOverlay   GtkPaned    GtkExpander    GtkFixed  */
  window = gtk_application_window_new (app);
  gtk_window_set_title (GTK_WINDOW (window), "Window");
  gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);

  box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);
  gtk_widget_set_halign (box, GTK_ALIGN_FILL);
  gtk_widget_set_valign (box, GTK_ALIGN_CENTER); /*  START  CENTER  END  FILL */
  gtk_window_set_child (GTK_WINDOW (window), box);

  button = gtk_button_new_with_label ("Hello World !");

  g_signal_connect (button, "clicked", G_CALLBACK (print), "Hi ! I'm there\n");
//  g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_window_destroy), window);

  gtk_box_append (GTK_BOX (box), button);

  gtk_window_present (GTK_WINDOW (window));
}

int main (int argc, char **argv) {
  GtkApplication *app;
  int status;

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_DEFAULT_FLAGS);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}