Some objects, such as Gdk::Pixmaps and
Pango::Fonts, are obtained from a shared store.
Therefore you cannot instantiate your own instances. These classes typically
inherit from Glib::Object. Rather than requiring you to
reference and unreference these objects, gtkmm uses the
RefPtr<> smartpointer.
Objects such as Gdk::Bitmap can only be instantiated
with a create() function. For instance,
Glib::RefPtr<Gdk::Bitmap> bitmap = Gdk::Bitmap::create(window, data, width, height);
You have no way of getting a bare Gdk::Bitmap. In the
example, bitmap is a smart pointer, so you can do this, much
like a normal pointer:
if(bitmap)
{
int depth = bitmap->get_depth().
}
When bitmap goes out of scope an
unref() will happen in the background and you don't need
to worry about it anymore. There's no new so there's no
delete.
If you copy a RefPtr, for instance
Glib::RefPtr<Gdk::Bitmap> bitmap2 = bitmap.
, or if you pass it as a method argument or a return type, then
RefPtr will do any necessary referencing to ensure that
the instance will not be destroyed until the last RefPtr
has gone out of scope.
See the appendix for detailed information about RefPtr.
If you wish to learn more about smartpointers, you might look in these books:
Bjarne Stroustrup, "The C++ Programming Language" - section 14.4.2
Nicolai M. Josuttis, "The C++ Standard Library" - section 4.2