gtk3 - correct application logic to get value of a setting from a GtkSettings object

[John Lumby <johnlumby hotmail com>]

Inside my gtk application,   I'd like to get (i.e. discover) the name of the current theme,which I believe is 
the  "gtk-theme-name"   property of the current window's  GtkSettings.
I see how to retrieve the  GtkSettings object ,  using  gtk_settings_get_default () or 
gtk_settings_get_for_screen (),but how do I extract the value of one element such as gtk-theme-name.
I see an api gtk_settings_set_property_value ()  which has no description but from its name sounds likethe 
write equivalent or a read of the property(???)  -  so I would want something like 
gtk_settings_get_property_value ()  -but there is no such api.
Cheers,    John Lumby