Can't set app icon

[Camilo Martin Culpian <camiloculpian gmail com>]

Hi I set mi app icon like this

try
    {
        Glib::RefPtr<Gtk::IconTheme> icon_theme =
Gtk::IconTheme::get_default();
        mi_app->set_icon(icon_theme->load_icon("mi_icon", 128,
Gtk::ICON_LOOKUP_USE_BUILTIN));
        //gtk_window_set_icon(this,icon_theme->load_icon("mi_icon", 48,
Gtk::ICON_LOOKUP_USE_BUILTIN));
    }catch(Glib::Error &e){std::cout<<"WARNING CAN't set app
icon....\n";}

but instead show the missing image icon.
i create the icon and place them in the app folder, in the theme i use.
what i'm doing wrong?
thanks in advance.

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