You can use C APIs which do not yet have convenient C++ interfaces.
It is generally not a problem to use C APIs from C++, and gtkmm helps by
providing access to the underlying C object, and providing an easy way to create
a C++ wrapper object from a C object, provided that the C API is also based on
the GObject system.
To use a gtkmm instance with a C function that requires a C
GObject instance, use the C++ instance’s
gobj() function to obtain a pointer to the underlying C
instance. For example:
Gtk::Button* button = new Gtk::Button("example");
gtk_button_do_something_that_gtkmm_cannot(button->gobj());
To obtain a gtkmm instance from a C GObject instance,
use one of the many overloaded Glib::wrap() functions.
The C instance’s reference count is not incremented, unless you set the optional
take_copy argument to true. For
example:
GtkButton* cbutton = get_a_button();
Gtk::Button* button = Glib::wrap(cbutton);
button->set_label("Now I speak C++ too!");
The C++ wrapper shall be explicitly deleted if
it's a widget or other class that inherits from Gtk::Object, and
the C instance has a floating reference when the wrapper is created, and
Gtk::manage() has not been called on it (which includes if it was created with Gtk::make_managed()), or
Gtk::manage() was called on it, but it was never added to, or was later removed from, its parent.
Glib::wrap() binds the C and C++ instances to each other.
Don't delete the C++ instance before you want the C instance to die.
In all other cases the C++ instance is automatically deleted when the last reference
to the C instance is dropped. This includes all Glib::wrap()
overloads that return a Glib::RefPtr.