Appendix A. The RefPtr smartpointer

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Glib::RefPtr is a smartpointer. Specifically, it is a reference-counting smartpointer. You might be familiar with std::unique_ptr<> and std::shared_ptr<>, which are also smartpointers. In gtkmm-4.0 Glib::RefPtr<> is an alias for std::shared_ptr<>, which is reference-counting. Glib::RefPtr<> was introduced long before there was a reference-counting smartpointer in the C++ Standard Library.

If you make your own Glib::ObjectBase-derived classes with create() methods that return a Glib::RefPtr, you must use Glib::make_refptr_for_instance() in your create() methods. This function creates a std::shared_ptr with a special deleter, which handles the reference-count for the wrapped C object.


A smartpointer acts much like a normal pointer. Here are a few examples.


You can copy RefPtrs, just like normal pointers. But unlike normal pointers, you don't need to worry about deleting the underlying instance.

auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
auto refPixbuf2 = refPixbuf;

Of course this means that you can store RefPtrs in standard containers, such as std::vector or std::list.

std::list<Glib::RefPtr<Gdk::Pixbuf>> listPixbufs;
auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);