Mail Archives: cygwin/2011/02/02/18:04:04
Hello Eric,
> > Here's a new proposal:
> > - Define a type 'wwchar_t' on all platforms, equivalent to uint32_t
> > on Windows platforms and to 'wchar_t' otherwise.
> > - Define functions 'mbrtowwc', 'iswwalpha', 'wwcwidth', and similar.
> > Their definition will be a trivial redirection to 'mbrtowc', 'iswalpha',
> > 'wcwidth' on most platforms, and a use of libunistring modules on
> > Windows platforms.
> ...
> Are you thinking of making a sane wrapping around either 4-byte wchar_t
> or which maps to 2-byte wchar_t but sanely handles UTF-16 (which makes
> it a thin wrapper on both Linux and Cygwin, but needing more work on
> mingw), or are you thinking that it is always a 4-byte type (needing
> lots more memory manipulation on cygwin to convert between 2- and 4-byte
> representations when using cygwin's functions, or else reimplementing
> everything from scratch by completely bypassing cygwin)?
I'm not sure I understand your question. The plan is that
- On platforms with a 32-bit wchar_t, like glibc, *BSD, and many others,
'wwchar_t' is identical to 'wchar_t', and the function wrappers are
simple redirections.
- On Cygwin and mingw, wwchar_t is 'uint32_t' (so as to accommodate
all Unicode characters and WEOF and so that it plays well with 'wint_t').
mbrtowwc is implemented by 1 or 2 calls to mbrtowc. mbsrtowwcs may be
implemented by a call to mbsrtowcs and an additional conversion loop,
or it might be implemented on top of mbrtowwc; that's merely a speed
vs. memory trade-off.
The plan is not to "completely bypassing cygwin", but to use as much
of Cygwin's built-ins as makes sense.
- On platforms with a 16-bit wchar_t but where the wchar_t[] encoding
in Unicode locales is merely UCS-2, like AIX, use the no-op thin
wrappers as well. If the platform does not support more than the BMP,
it makes not much sense for GNU programs to try to work around that.
> As to the name: I agree the opinion of others that xchar_t is easier to
> type and easier to avoid typos of a missing 'w' than wwchar_t.
If a developer makes a typo here, he's likely to get a gcc warning or
a link error. But yes, it's possible to pass a 'wwchar_t' to
iswalpha(), which will yield wrong results. I don't think this risk
can be much reduced through a different name.
> gnulib already has xprintf as a counterpart to xmalloc (which calls
> exit() if the printf fails for memory allocation or other non-I/O
> related reasons), so we can't blindly use 'x'
Good point. The 'x' prefix has already several meanings in gnulib:
- checking against memory allocation failure,
- checking against errors,
- no size limitation,
- a more convenient interface,
- a wrapper that prints an error message.
It doesn't seem wise to add another meaning to it.
Thanks for the feedback.
--
In memoriam Carl Friedrich Goerdeler <http://en.wikipedia.org/wiki/Carl_Friedrich_Goerdeler>
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