title: Gtk+3 &C & Glade problems
body: <p>I tried to make a simple Gui program with C and Glade on Linux.
  I wrote a simple program and design a window with Glade.
  When I run the code it says:</p>
  
  <pre><code>(gtk-test:23026): Gtk-CRITICAL **: gtk_widget_show: assertion ‘GTK_IS_WIDGET(widget)’ failed
  </code></pre>
  
  <p>And no Window open.
  I searched a bit on the internet but I cant anything helpful. Some say that I have to convert the glade file to .xml but that didn't work.</p>
  
  <h2>C</h2>
  
  <pre><code>#include &lt;gtk/gtk.h&gt;
  
  int main(int argc, char *argv[])
  {
      GtkBuilder      *builder; 
      GtkWidget       *window;
  
      gtk_init(&amp;argc, &amp;argv);
  
      builder = gtk_builder_new();
      gtk_builder_add_from_file (builder, "window_main.glade", NULL);
  
      window = GTK_WIDGET(gtk_builder_get_object(builder, "window_main"));
      gtk_builder_connect_signals(builder, NULL);
  
      g_object_unref(builder);
  
      gtk_widget_show(window);                
      gtk_main();
  
      return 0;
  }
  
  void on_window_main_destroy()
  {
      gtk_main_quit();
  }
  </code></pre>
  
  <h2>Glade</h2>
  
  <pre><code>&lt;?xml version=1.0 encoding="UFT-8"?&gt;
  &lt;!-- Generated with glade 3.18.3 --&gt;
  &lt;interface&gt;
      &lt;requires lib="gtk+" version="3.12"/&gt;
      &lt;object class="GtkWindow" id="window_main"&gt;
          &lt;property name="can_focus"&gt;False&lt;/property&gt;
          &lt;property name="title" translatable="yes"&gt;Test Window&lt;/property&gt;
          &lt;property name="default_width"&gt;640&lt;/property&gt;
          &lt;property name="default_height"&gt;480&lt;/property&gt;
          &lt;signal name="destroy" handler="on_window_main_destroy" swapped="no"/&gt;
          &lt;child&gt;
              &lt;placeholder/&gt;
          &lt;/child&gt;
      &lt;/object&gt;
  &lt;/interface&gt;
  </code></pre>