Mixing C and C++ APIs

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("example");

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

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.