> It would make sense if scanf() had the equivalent flag to printf() to
> make number printing and parsing at least potentially orthogonal.
>

That is not an easy thing to do because of local (er, locale:)
conventions.  See
https://docs.oracle.com/cd/E19455-01/806-0169/overview-9/index.html for
examples.

Having a canonical input and output format, which is converted by filters
just before/after the human sees the numbers, seems the only way to make
this work globally.