According to POSIX, The mbtowc() function shall fail if:
[EILSEQ] An invalid character sequence is detected.
Reviewed by: bapt
Differential Revision: https://reviews.freebsd.org/D5496
Obtained from: OpenBSD (Ingo Schwarze)
MFC after: 1 month
load of _l suffixed versions of various standard library functions that use
the global locale, making them take an explicit locale parameter. Also
adds support for per-thread locales. This work was funded by the FreeBSD
Foundation.
Please test any code you have that uses the C standard locale functions!
Reviewed by: das (gdtoa changes)
Approved by: dim (mentor)
return -1 regardless of what s points to, mbtowc(&w, s, 1) sets w to a
null wide character when s points to a null byte. This seems to be closer
to what most other implementations do, but the C99 standard contradicts
itself for these cases.