c - Getting keyboard modifiers state using Gnome libs (GDK) fetches initial state only

Question

I'm trying to get the current keyboard modifiers state through gnome GDK or GTK library in aim to implement an accessibility gnome shell extension that shows that state.

I know how to get thier state using xlib, but there is not full binding for gnome gjs.

The code below get only the initial state. It does not update state.

/*
 * compiling: gcc `pkg-config --cflags gdk-3.0` -o gdk_mod gdk_mod.c `pkg-config --libs gdk-3.0`
 */

#include <gdk/gdk.h>

int main (int argc, char **argv) {

    gdk_init(&argc, &argv);

    GdkDisplay * disp;
    disp = gdk_display_open(NULL);
    if (disp!=NULL) g_printf("display connected!
");

    GdkKeymap * kmap;
    kmap = gdk_keymap_get_for_display(disp);

    guint state;
    state = gdk_keymap_get_modifier_state(kmap);
    g_printf("mod state: %x
", state);

    while (1) {
        g_usleep(1000000);
        //kmap = gdk_keymap_get_for_display(disp);
        state = gdk_keymap_get_modifier_state(kmap);
        g_printf("mod state: %x
", state);
    }

}

Here an example output with CAPS lock active then inactive but no change:

$ ./gdk_mod 
display found!
mod state: 2
mod state: 2
mod state: 2
mod state: 2
mod state: 2
^C

Currently using Kubuntu 15.04.

What's wrong with my code?

Answer 1

• Indeed, I need an event loop as andlabs said in his comment. His suggestion to use GTK gtk_init() & gtk_main() works perfectly.

  /*
   * compiling: gcc `pkg-config --cflags gtk+-3.0` -o gtk_xkbmod3 gtk_xkbmod3.c `pkg-config --libs gtk+-3.0`
   */
  
  #include <gtk/gtk.h>
  
  static void update(GdkKeymap * kmap) {
      guint state;
      state = gdk_keymap_get_modifier_state(kmap);
      g_printf("%i
  ", state);
  }
  
  int main (int argc, char **argv) {
  
      gtk_init(&argc, &argv);
  
      GdkKeymap * kmap;
      kmap = gdk_keymap_get_default();
  
      g_timeout_add_seconds(1, (GSourceFunc) update, kmap);
  
      gtk_main();
  
  }
  

• I could also use GDK with GLib GMainLoop.

  /*
   * compiling: gcc `pkg-config --cflags gdk-3.0` -o gdk_xkbmod4 gdk_xkbmod4.c `pkg-config --libs gdk-3.0`
   */
  
  #include <gdk/gdk.h>
  
  GMainLoop *mainloop;
  
  static void update(GdkKeymap * kmap) {
      guint state;
      state = gdk_keymap_get_modifier_state(kmap);
      g_printf("%i
  ", state);
  }
  
  int main (int argc, char **argv) {    
  
      gdk_init(&argc, &argv);
  
      GdkKeymap * kmap;
      kmap = gdk_keymap_get_default();
  
      g_timeout_add_seconds(1, (GSourceFunc) update, kmap);
  
      mainloop = g_main_loop_new(g_main_context_default(), FALSE);
      g_main_loop_run(mainloop);    
  }
  

References:

• Xfce Foundation Classes: The Main Event Loop
• GTK+ Forums: GDK + GLib main loop