[PATCH 01/15] stdio-common: Don't read real input beyond the field width in scanf [BZ #13988]

[Maciej W. Rozycki]

On Fri, 25 Apr 2025, Joseph Myers wrote:

> > 1. My understanding of ISO C is that the field width limit is given in
> >    terms of (possibly multibyte) characters rather than bytes ("[...] that 
> >    specifies the maximum field width (in characters)") for all the 
> >    conversions except for %c, %s, %[ for which the field width limit is 
> >    given in bytes ("the extent of the input field is determined on a 
> >    byte-by-byte basis").  Our code seems to implement it the other way 
> >    round though.
> > 
> >    Have I got my understanding backwards?  Am I missing something here?
> 
> "character" means "byte" in ISO C unless explicitly preceded by a 
> qualification such as "multibyte".  So width is given in bytes (for narrow 
> scanf functions as opposed to those in <wchar.h>).

 Right, thanks, cf. 3.7.1 as at C23, but it makes me wonder why footnote 
349 is needed then that just reinstates what 3.7.1 says.  And indeed it 
seems wrong to me that say with '%<w>lc' and 'fscanf' <w> counts in terms 
of multibyte characters rather than bytes, contrary to said footnote.  

 Thoughts?

  Maciej