guint gtk_get_major_version ( void )
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.