GTK C++: Could not find signal handler Did you compile with -rdynamic?

I am new at GTK programming and I am facing the following issue. I can compile the code without any warnings or errors however when I execute the binary I get this massage and the button does not work. The error looks like this:

(project:9686): Gtk-WARNING **: 16:26:31.359: Could not find signal handler ‘on_button_clicked’. Did you compile with -rdynamic?

That is the code:

#include <gtk/gtk.h>

 static const gchar *interface = 
 "<interface>"
 "  <object class="GtkWindow" id="main-window">"
 "    <signal name="destroy" handler="gtk_main_quit"/>"
 "    <child>"
 "      <object class="GtkButton" id="my-button">"
 "        <property name="label">Hallo, Welt!</property>"
 "        <signal name="clicked" handler="on_button_clicked"/>"
 "      </object>"
 "    </child>"
 "  </object>"
 "</interface>";

G_MODULE_EXPORT void on_button_clicked (GtkWidget *w, gpointer d)
{
    g_print ("Hallo, Welt!n");
}

int main (int argc, char *argv[])
{
    GtkBuilder *builder;
    GError *error = NULL;
    GtkWidget *window;

    gtk_init (&argc, &argv);
    builder = gtk_builder_new ();
    gtk_builder_add_from_string (builder, interface, -1, &error);
    gtk_builder_connect_signals (builder, NULL);
    window = GTK_WIDGET(gtk_builder_get_object (builder, "main-window"));
    gtk_widget_show_all (window);
    gtk_main ();
    return 0;
}

I am working at a Linux machine and I compiled in the terminal with the following command:

g++ -Wall -std=c++0x project.cpp `pkg-config --cflags --libs gtk+-3.0 gmodule-2.0` -o project

I tried to compile with:

• -rdynamic
• -Wl,–export-dynamic
• -lgmodule-2.0
• pkg-config --cflags --libs gtk+-3.0 gmodule-no-export-2.0

but nothing worked.

Answer

It’s hard to know for sure, but I would guess the problem is that you are compiling using a C++ compiler whereas your example is written in C. The C++ compiler is “mangling” the names of your exported symbols. If you aren’t writing the rest of your program in C++, then I would recommend compiling with gcc -std=c99 instead of g++ -std=c++0x.

On the other hand, if the rest of your program does need to be written in C++, then you will need to prefix every symbol that you want to export for GtkBuilder (which does not know about C++ name mangling) with extern "C", or place them all together inside one or more extern "C" { ... } blocks. This will prevent the name from being mangled, so then GtkBuilder will be able to find it.

To check whether this is the case, try running nm -g | grep on_button_clicked (without any “demangle” option) on your compiled file. If the name is mangled, you will see something like __Z17on_button_clicked13BLAH14BLAH whereas if it is not, then you will just see _on_button_clicked.