how to add a ComboBox into toolbar?

["Shuduo Sang" <sangshuduo gmail com>]

Hi,

I'd like to add a GtkComboBox into a toolbar, but I can't see it even
no error reported.
My code is following,

...
GtkWidget *combo;
GList *items = NULL;
items = g_list_append(items, "aaa");
items = g_list_append(items, "bbb");

combo = gtk_combo_new();
gtk_combo_set_popdown_strings(GTK_COMBO(combo), items);
gtk_toolbar_insert(GTK_BOOLBAR(toolbar), combo, 0);
...

I googled GtkComboBox example code but failed.
Could anyone give me a hit on this?
Very appreciated for your help.

Shuduo