The “GVariant Format Strings” section[0] of the documentation is generally a very useful reference for how to construct and deconstruct GVariants of different types. But the section on dictionaries[1] only shows how to construct a dictionary – it does not show how to extract a dictionary, and extract entries from it.

For a motivating example, suppose you are handling org.freedesktop.DBus.ObjectManager.InterfacesAdded and for some reason are not using generated code. You get a GVariant of type "(oa{sa{sv})" and you want to do the equivalent of v[1]["com.example.Foo"]["Bar"] to pluck a property out of the dictionary. How do you do it?

I believe the answer is something like:

  GVariant *a;
  GVariant *c;
  GVariantDict d;
  guint32 e;

  g_variant_get (v, "(oa{?*})", NULL, &a);

  c = g_variant_lookup_value (a, "com.example.Foo", "a{sv}");
  
  g_variant_dict_init (&d, c);
  g_variant_dict_lookup (&d, "Bar", "u", &e);

and if you wanted to get many values from the outer, non-vardict dictionary, you'd want to scan it with GVariantIter.

[0] https://developer.gnome.org/glib/stable/gvariant-format-strings.html
[1] https://developer.gnome.org/glib/stable/gvariant-format-strings.html#gvariant-format-strings-dictionaries