How to merge Gtk+ builder

Question

I'm building a GTK+ gui and I'm trying to use the GtkBuilder to do it.

There is a main window in which there is a notebook, a menu and two buttons. I want to fill the notebook with tabs when I click on a button.

So I created the main window from a file with a GtkBuilder, and then I try to add each tab to the builder.

For now, I did this (the unindented code are debug print):

#include <stdio.h>
#include <stdlib.h>

#include <string.h>

#include <gtk/gtk.h>

#include "main.h"

GtkBuilder* build;
int i;

#define TAB\
  "<interface>\
    <object class=\"GtkNotebook\" id=\"note\">\
      <property name=\"scrollable\">t</property>\
      <property name=\"show-border\">t</property>\
      <property name=\"show-tabs\">t</property>\
      <child>\
        <object class=\"GtkLabel\" id=\"tab%d\">\
          <property name=\"label\">Content%d</property>\
        </object>\
      </child>\
      <child type=\"tab\">\
        <object class=\"GtkLabel\" id=\"labTab%d\">\
          <property name=\"label\">Label%d</property>\
        </object>\
      </child>\
    </object>\
  </interface>"

int main(int argc, char** argv) {
  GtkWidget* window;
//  GtkWidget* item;
  GError* error=NULL;
  GtkAccelGroup* accel_group;

  i=0;

  gtk_init(&argc, &argv);

  build=gtk_builder_new();
  if (gtk_builder_add_from_file(build, "gui.ui", &error)==0)
    printf("erreur %s\n", error->message);

  gtk_builder_add_callback_symbol(build, "quit", func);
  gtk_builder_add_callback_symbol(build, "add", add);

  gtk_builder_connect_signals(build, NULL);

  window=(GtkWidget*)gtk_builder_get_object(build, "main");
  gtk_window_maximize(GTK_WINDOW(window));

  gtk_widget_show_all(window);

  gtk_main();


  return EXIT_SUCCESS;
}

void add() {
  char* str;
  GtkWidget* window;
  GError* error=NULL;
  FILE* file=NULL;

printf("in add 1\n");
  if ((str=malloc(sizeof(TAB)+20))==NULL) {
    perror("malloc");
    exit(EXIT_FAILURE);
  }
printf("in add 2\n");

  snprintf(str, sizeof(TAB)+20, TAB, i, i, i, i);
printf("in add 3, str : %s\n", str);

  if ((file=fopen("tmp.ui", "w"))==NULL) {
    free(str);
    perror("fopen");
    exit(EXIT_FAILURE);
  }

  fprintf(file, TAB, i, i, i, i);

  fclose(file);

/*  if (gtk_builder_add_from_file(build, "tmp.ui", &error)==0)
    printf("erreur %s\n", error->message);*/
  if (gtk_builder_add_from_string(build, str, sizeof(str), &error)==0)
    printf("erreur %s\n", error->message);
printf("in add 4\n");

  if ((window=(GtkWidget*)gtk_builder_get_object(build, "main"))==NULL)
    printf("Can't find\n");
  else
    gtk_widget_show_all(window);

  sprintf(str, "tab%d", i);
  if ((window=(GtkWidget*)gtk_builder_get_object(build, str))==NULL)
    printf("in add, Does not exist (%s)\n", str);
  else
    printf("in add, Exist (%s)\n", str);

  remove("tmp.ui");
  free(str);
  ++i;
//  free(error);
}

Here is my builder definition:

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <!-- Main window -->
  <object class="GtkWindow" id="main">
    <property name="title">Test Xml</property>
    <property name="window-position">GTK_WIN_POS_CENTER</property>
    <property name="default-width">1024</property>
    <property name="default-height">512</property>
    <signal name="delete-event" handler="quit"/>

    <child>
      <object class="GtkBox" id="mainBox">
        <property name="orientation">GTK_ORIENTATION_VERTICAL</property>
        <property name="spacing">5</property>

        <!-- Menu -->
        <child>
          <object class="GtkMenuBar" id="menuBar">
            <child>

              <!-- Menu fichier -->
              <object class="GtkMenuItem" id="m1">
                <property name="label">_Fichier</property>
                <property name="use_underline">True</property>
                <child type="submenu">
                  <object class="GtkMenu" id="menu">
                    <property name="accel-group">accel_group</property>
                    <child>

                      <!-- Item Quitter -->
                      <object class="GtkMenuItem" id="i1">
                        <property name="accel-path">&lt;Test&gt;/FILE/QUIT</property>
                        <property name="label">_Quitter</property>
                        <property name="use_underline">True</property>
                        <signal name="activate" handler="quit"/>
                      </object>
                      <!-- End Item Quitter -->

                    </child>
                  </object>
                </child>
              </object>
              <!-- End Menu fichier -->

            </child>
          </object>
        </child>
        <!-- End Menu -->

        <!-- Frame -->
        <child>
          <object class="GtkFrame" id="mainframe">
            <property name="expand">t</property>

            <!-- Note book -->
            <child>
              <object class="GtkNotebook" id="note">
                <property name="scrollable">t</property>
                <property name="show-border">t</property>
                <property name="show-tabs">t</property>
              </object>
            </child>
            <!-- Note book -->
          </object>
        </child>
        <!-- End Frame -->

        <!-- Bottom box -->
        <child>
          <object class="GtkBox" id="bottomBox">
            <property name="orientation">GTK_ORIENTATION_HORIZONTAL</property>
            <property name="spacing">5</property>

            <!-- Buttons -->
            <child>
              <object class="GtkButton" id="boutonPlus">
                <property name="label">_Ajouter</property>
                <property name="use-underline">t</property>
                <signal name="activate" handler="add"/>
              </object>
            </child>
            <child>
              <object class="GtkButton" id="boutonMoins">
                <property name="label">_Enlever</property>
                <property name="use-underline">t</property>
              </object>
            </child>
            <!-- End buttons -->
          </object>
        </child>
        <!-- End Bottom box -->
      </object>
    </child>
  </object>
</interface>

And here is the output:

in add 1
in add 2
in add 3, str : <interface>
    <object class="GtkNotebook" id="note">
      <property name="scrollable">t</property>
      <property name="show-border">t</property>
      <property name="show-tabs">t</property>
      <child>
        <object class="GtkLabel" id="tab0">
          <property name="label">Content0</property>
        </object>
      </child>
      <child type="tab">
        <object class="GtkLabel" id="labTab0">
          <property name="label">Label0</property>
        </object>
      </child>
    </object>
  </interface>
in add 4
in add, Does not exist (tab0)

As we can see, the tab is not add in the builder, but it seems there is no error when I add it.

• In the documentation it's said that, in case we want to merge some ui definitions we must use gtk_builder_new(), and then use gtk_builder_add_from_...(). So I did it, and in my add function, I try to add tab from string or from file just to see the problem was because I start to add from file and then from string, but it does not.
• In the documentation, I didn't find anything about what it's needed to do the merge. So, to add the tab, I tried with/without the <interface> and the nodebook definition. But it didn't change anything.

Is there some documentations about merging ui definitions with a GtkBulder, or can someone explain me what I'm doing wrong ?