[Bug libstdc++/37475] codecvt::do_in/do_out functions return "ok" when the output sequence has zero length

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37475

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Kristian Spangsege from comment #7)
> Curiously, this bug does not occur when using the Cygwin or MinGW versions
> of GCC. In these cases, the result is `partial` as it should be. I assume
> this is because on Cygwin and MinGW, libstdc++ uses a generic locale
> implementation that is different from the one ordinarily used on Linux.

It has an explicit check for this condition:

    // It is not clear that __from < __from_end implies __ret != ok
    // (see DR 382).
    if (__ret == ok && __from < __from_end)
      __ret = partial;