public uint get_major_version ()
Returns the major version number of the GTK library.
(e.g. in GTK version 3.1.5 this is 3.)
This function is in the library, so it represents the GTK library your code is running against. Contrast with the gtk_major_version macro, which represents the major version of the GTK headers you have included when compiling your code.
the major version number of the GTK library