GtkObject The base class of the GTK+ type hierarchy #GtkObject is the base class for all widgets, and for a few non-widget objects such as #GtkAdjustment. #GtkObject predates #GObject; non-widgets that derive from #GtkObject rather than #GObject do so for backward compatibility reasons. #GtkObjects are created with a "floating" reference count. This means that the initial reference is not owned by anyone. Calling g_object_unref() on a newly-created #GtkObject is incorrect, the floating reference has to be removed first. This can be done by anyone at any time, by calling g_object_ref_sink() to convert the floating reference into a regular reference. g_object_ref_sink() returns a new reference if an object is already sunk (has no floating reference). When you add a widget to its parent container, the parent container will do this: g_object_ref_sink (G_OBJECT (child_widget)); This means that the container now owns a reference to the child widget and the child widget has no floating reference. The purpose of the floating reference is to keep the child widget alive until you add it to a parent container: button = gtk_button_new (); /* button has one floating reference to keep it alive */ gtk_container_add (GTK_CONTAINER (container), button); /* button has one non-floating reference owned by the container */ #GtkWindow is a special case, because GTK+ itself will ref/sink it on creation. That is, after calling gtk_window_new(), the #GtkWindow will have one reference which is owned by GTK+, and no floating references. One more factor comes into play: the "destroy" signal, emitted by the gtk_object_destroy() method. The "destroy" signal asks all code owning a reference to an object to release said reference. So, for example, if you call gtk_object_destroy() on a #GtkWindow, GTK+ will release the reference count that it owns; if you call gtk_object_destroy() on a #GtkButton, then the button will be removed from its parent container and the parent container will release its reference to the button. Because these references are released, calling gtk_object_destroy() should result in freeing all memory associated with an object, unless some buggy code fails to release its references in response to the "destroy" signal. Freeing memory (referred to as finalization only happens if the reference count reaches zero. Some simple rules for handling #GtkObject: Never call g_object_unref() unless you have previously called g_object_ref(), even if you created the #GtkObject. (Note: this is not true for #GObject; for #GObject, the creator of the object owns a reference.) Call gtk_object_destroy() to get rid of most objects in most cases. In particular, widgets are almost always destroyed in this way. Because of the floating reference count, you don't need to worry about reference counting for widgets and toplevel windows, unless you explicitly call g_object_ref() yourself. #GObject The object itself. You should never use these members directly - use the accessing macros instead. Signals that all holders of a reference to the #GtkObject should release the reference that they hold. May result in finalization of the object if all references are released. @object: the object which received the signal. Tells about the state of the object. @GTK_IN_DESTRUCTION: the object is currently being destroyed. This is used internally by GTK+ to prevent reinvokations during destruction. @GTK_RESERVED_1: @GTK_RESERVED_2: reserved for future use Gets the #GtkObjectFlags for an object without directly accessing its members. @obj: the object whose flags are returned. Emits the "destroy" signal notifying all reference holders that they should release the #GtkObject. See the overview documentation at the top of the page for more details. The memory for the object itself won't be deleted until its reference count actually drops to 0; gtk_object_destroy() merely asks reference holders to release their references, it does not free the object. @object: the object to destroy.