pub fn major_version() -> u32
Returns the major version number of the GTK library.
For example, 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
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