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When construcing a more complicated user interface, with dozens or hundreds of widgets, doing all the setup work in C code is cumbersome, and making changes becomes next to impossible.
Thankfully, GTK+ supports the separation of user interface layout from your business logic, by using UI descriptions in an XML format that can be parsed by the GtkBuilder class.
Example 3. Packing buttons with GtkBuilder
Create a new file with the following content named example-4.c.
#include <gtk/gtk.h>
static void
print_hello (GtkWidget *widget,
             gpointer   data)
{
  g_print ("Hello World\n");
}
int
main (int   argc,
      char *argv[])
{
  GtkBuilder *builder;
  GObject *window;
  GObject *button;
  gtk_init (&argc, &argv);
  /* Construct a GtkBuilder instance and load our UI description */
  builder = gtk_builder_new ();
  gtk_builder_add_from_file (builder, "builder.ui", NULL);
  /* Connect signal handlers to the constructed widgets. */
  window = gtk_builder_get_object (builder, "window");
  g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
  button = gtk_builder_get_object (builder, "button1");
  g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);
  button = gtk_builder_get_object (builder, "button2");
  g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);
  button = gtk_builder_get_object (builder, "quit");
  g_signal_connect (button, "clicked", G_CALLBACK (gtk_main_quit), NULL);
  gtk_main ();
  return 0;
}
Create a new file with the following content named builder.ui.
<interface>
  <object id="window" class="GtkWindow">
    <property name="visible">True</property>
    <property name="title">Grid</property>
    <property name="border-width">10</property>
    <child>
      <object id="grid" class="GtkGrid">
        <property name="visible">True</property>
        <child>
          <object id="button1" class="GtkButton">
            <property name="visible">True</property>
            <property name="label">Button 1</property>
          </object>
          <packing>
            <property name="left-attach">0</property>
            <property name="top-attach">0</property>
          </packing>
        </child>
        <child>
          <object id="button2" class="GtkButton">
            <property name="visible">True</property>
            <property name="label">Button 2</property>
          </object>
          <packing>
            <property name="left-attach">1</property>
            <property name="top-attach">0</property>
          </packing>
        </child>
        <child>
          <object id="quit" class="GtkButton">
            <property name="visible">True</property>
            <property name="label">Quit</property>
          </object>
          <packing>
            <property name="left-attach">0</property>
            <property name="top-attach">1</property>
            <property name="width">2</property>
          </packing>
        </child>
      </object>
      <packing>
      </packing>
    </child>
  </object>
</interface>
You can compile the program above with GCC using:
        gcc `pkg-config --cflags gtk+-3.0` -o example-4 example-4.c `pkg-config --libs gtk+-3.0`
      
Note that GtkBuilder can also be used to construct objects
    that are not widgets, such as tree models, adjustments, etc.
    That is the reason the method we use here is called
    gtk_builder_get_object() and returns a GObject* instead of a
    GtkWidget*.
Normally, you would pass a full path to
    gtk_builder_add_from_file() to make the execution of your program
    independent of the current directory. A common location to install
    UI descriptions and similar data is
    /usr/share/.
    appname
It is also possible to embed the UI description in the source
    code as a string and use gtk_builder_add_from_string() to load it.
    But keeping the UI description in a separate file has several
    advantages: It is then possible to make minor adjustments to the UI
    without recompiling your program, and, more importantly, graphical
    UI editors such as glade
    can load the file and allow you to create and modify your UI by
    point-and-click.