How to set application flags?

[Радомир Хаџић <radomirhadzic46 gmail com>]

Hello. I have a small problem. I need to set application flags yet I don't know how.

Here is my attempt based on some source code I read:

#include <gtkmm/application.h>

int main(int argc, char **argv)
{
    Glib::RefPtr<Gtk::Application> app = Gtk::Application::create(argc, argv, "org.gtkmm.example");
    app->set_flags(Gio::Application::Flags::NON_UNIQUE);
    return app->run();
}

The error I'm getting is:

test.cpp:6:35: error: ‘Gio::Application::Flags’ has not been declared
app->set_flags(Gio::Application::Flags::NON_UNIQUE);

                                                  ^~~~~

That obviously means that there is no Flags in Gio::Application, but why?

Thank you for reading this and I'll hope you'll be able to help me.