How does GTK Statusbar work? What's wrong with my code?

Question

Dear developers,

I would like to have a statusbar, so I started by making a small program with just a statusbar, so I could see how it worked.

Right now I would just like to be able to get some text in it, but it shows a random character instead.

Can someone see what's wrong with my code?

#include <gtk/gtk.h>

int main (int argc, char *argv[]) {
  GtkWidget *window, *statusbar, *vbox;
  gchar *info;
  gtk_init(&argc, &argv);

  window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
  gtk_widget_set_size_request(window, 250, -1);

  g_signal_connect(G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL);

  statusbar = gtk_statusbar_new();

  /* stack for info messages */
  g_object_set_data(G_OBJECT(statusbar), "info", (gpointer) "1");
  g_object_set_data(G_OBJECT(statusbar), "info", (gpointer) "2");
  g_object_set_data(G_OBJECT(statusbar), "info", (gpointer) "3");

  /* stack for warning messages */
  g_object_set_data(G_OBJECT(statusbar), "warning", (gpointer) "A");
  g_object_set_data(G_OBJECT(statusbar), "warning", (gpointer) "B");
  g_object_set_data(G_OBJECT(statusbar), "warning", (gpointer) "C");

  /* get id for the message at the top of the info stack? */
  guint id = gtk_statusbar_get_context_id(statusbar, "info");
  /* show the top message from the info stack ? */
  gtk_statusbar_push(statusbar, id, info);

  vbox = gtk_vbox_new(FALSE, 5);  
  gtk_box_pack_start_defaults(GTK_BOX (vbox), statusbar);
  gtk_container_add(GTK_CONTAINER(window), vbox);

  gtk_widget_show_all(window);
  gtk_main();
  return 0;
}

I get these warnings

s.c:26: warning: passing argument 1 of ‘gtk_statusbar_get_context_id’ from incompatible pointer type
/usr/include/gtk-2.0/gtk/gtkstatusbar.h:94: note: expected ‘struct GtkStatusbar *’ but argument is of type ‘struct GtkWidget *’
s.c:28: warning: passing argument 1 of ‘gtk_statusbar_pop’ from incompatible pointer type
/usr/include/gtk-2.0/gtk/gtkstatusbar.h:100: note: expected ‘struct GtkStatusbar *’ but argument is of type ‘struct GtkWidget *’
s.c:28: error: too many arguments to function ‘gtk_statusbar_pop’

Answer 1

You declared GtkWidget *statusbar but the gtk_statusbar_... methods expect GtkStatusbar *: casting it with GTK_STATUSBAR(statusbar) removes the warnings. This is not a big issue as the program would work anyway: the biggest problem is you're using info without initializing it.

The following code is working as expected here:

/* gcc -o status status.c $(pkg-config --cflags --libs gtk+-2.0) */

#include <gtk/gtk.h>

int main (int argc, char *argv[]) {
    GtkWidget *window, *statusbar, *vbox;
    gchar *info;
    gtk_init(&argc, &argv);

    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_widget_set_size_request(window, 250, -1);

    g_signal_connect(G_OBJECT(window), "destroy",
                     G_CALLBACK(gtk_main_quit), NULL);

    statusbar = gtk_statusbar_new();

    /* stack for info messages */
    g_object_set_data(G_OBJECT(statusbar), "info", (gpointer)
                      "1");
    g_object_set_data(G_OBJECT(statusbar), "info",
                      (gpointer) "2");
    g_object_set_data(G_OBJECT(statusbar), "info",
                      (gpointer) "3");

    /* stack for warning messages */
    g_object_set_data(G_OBJECT(statusbar), "warning",
                      (gpointer) "A");
    g_object_set_data(G_OBJECT(statusbar), "warning",
                      (gpointer) "B");
    g_object_set_data(G_OBJECT(statusbar),
                      "warning", (gpointer) "C");

    /* get id for the message at the top of the
     * info stack? */
    guint id = gtk_statusbar_get_context_id(GTK_STATUSBAR(statusbar), "info");
    /* show the top message from the info stack
     * ? */
    info = "This was uninitialized";
    gtk_statusbar_push(GTK_STATUSBAR(statusbar), id, info);

    vbox = gtk_vbox_new(FALSE, 5);
    gtk_box_pack_start_defaults(GTK_BOX
                                (vbox),
                                statusbar);
    gtk_container_add(GTK_CONTAINER(window),
                      vbox);

    gtk_widget_show_all(window);
    gtk_main();
    return 0;
}

I don't know what are you trying to achieve with g_object_set_data though, but maybe they are only old tests...

Addenum:

You should use gtk_statusbar_push() to pile up messages on the status bar stack. With gtk_statusbar_pop() you'll remove the last pushed message, discovering the previous one.

gtk_statusbar_push(GTK_STATUSBAR(statusbar), id, "First message");
// Now the statusbar shows "First message"
gtk_statusbar_push(GTK_STATUSBAR(statusbar), id, "Second message");
// Now the statusbar shows "Second message"
gtk_statusbar_pop(GTK_STATUSBAR(statusbar), id);
// Now the statusbar shows "First message"