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I am using this tutorial for GTK learning. The second example in that link uses the two functions: g_signal_connect and g_signal_connect_swapped. I don't see any differences in the calling of the two functions, but I found the following in the gsignal.h (this can also be found here):

    For example, this allows the shorter code:
    |[<!-- language="C" -->
    g_signal_connect_swapped (button, "clicked",
                              (GCallback) gtk_widget_hide, other_widget);
    ]|

    Rather than the cumbersome:
    |[<!-- language="C" -->
    static void
    button_clicked_cb (GtkButton *button, GtkWidget *other_widget)
    {
        gtk_widget_hide (other_widget);
    }

    …

    g_signal_connect (button, "clicked",
                      (GCallback) button_clicked_cb, other_widget);
    ]|

When I compile the code with the g_signal_connect_swapped replaced with g_signal_connect, the program will not work properly; however, if I do the opposite thing, it still works. Can anyone tell me what is the differences between the two functions? Also, if confusion is not wanted, is it better to always use g_signal_connect_swapped instead of the other?

EDIT: The code for the "second example":

    #include <gtk/gtk.h>

    static void
    print_hello (GtkWidget *widget,
                 gpointer   data)
    {
      g_print ("Hello World\n");
    }

    static void
    activate (GtkApplication *app,
              gpointer        user_data)
    {
      GtkWidget *window;
      GtkWidget *button;
      GtkWidget *button_box;

      window = gtk_application_window_new (app);
      gtk_window_set_title (GTK_WINDOW (window), "Window");
      gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);

      button_box = gtk_button_box_new (GTK_ORIENTATION_HORIZONTAL);
      gtk_container_add (GTK_CONTAINER (window), button_box);

      button = gtk_button_new_with_label ("Hello World");
      g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);
      g_signal_connect_swapped (button, "clicked", G_CALLBACK (gtk_widget_destroy), window);
      gtk_container_add (GTK_CONTAINER (button_box), button);

      gtk_widget_show_all (window);
    }

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

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

      return status;
    }
Chromium
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  • "The program will not work properly..." Can you explain what you expected to see and what you actually saw? – ptomato Mar 24 '16 at 05:01
  • Well, originally, it is designed to close the window and also print a string "Hello World" on the terminal. If I changed the functions, the button will disappear, but the window is not closed – Chromium Mar 24 '16 at 09:10
  • So according to the [post](http://stackoverflow.com/questions/2171724/what-does-g-signal-connect-swapped-do), is that the `g_signal_connect_swapped` passes the last parameter to the callback function? Like in that post, it passes the `textview` as parameter to `gtk_widget_hide()`? – Chromium Mar 24 '16 at 12:15

0 Answers0