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Re: 16-bit wchar_t on Windows and Cygwin
On Feb 2 17:02, Bruno Haible wrote:
> Hello Corinna,
> > And, please note the wording in SUSv4, for instance in
> > http://calimero.vinschen.de/susv4/functions/iswalpha.html
> Likewise in POSIX:2008, at the URL
Oops, sorry for the wrong URL! I'm using a local copy of SUSv4 for
speed, but forgot that entirely when copy/pasting it.
> > The wc argument is a wint_t, the value of which the application shall
> > ^^^^^^ ^^^^^^^^^^^
> > ensure is a wide-character code corresponding to a valid character in
> > the current locale, or equal to the value of the macro WEOF. If the
> > argument has any other value, the behavior is undefined.
> What this sentence means in formulas, is that when an application passes
> a 'wint_t x' to iswalpha(), it has to satisfy
> x == (wint_t) (wchar_t) x || x == EOF
Sure, I agree. But it doesn't say this *exactly*, so I took the liberty
to stretch the limits a bit so that there is *some* way for applications
to use the wctype functions despite using UTF-16 and despite having a
> > iswalpha takes wint_t, not wchar_t. Since sizeof (wint_t) is 4 byte,
> > the function can return the correct value, provided that the application
> > converts the UTF-16 surrogate to UTF-32 before calling iswalpha.
> When an application does this, is passes an invalid wint_t value to
> iswalpha(), according to the spec paragraph that you have just cited.
> So the application uses an extension to POSIX functionality, not
> POSIX itself.
Well, given that the description doesn't explicitely talk about a value
given as wchar_t, but instead about a "wide-character code corresponding
to a valid character" I saw some room for interpretation...
> I see that Cygwin 1.7.x iswalpha() works in this way you describe (but
> mingw's iswalpha() doesn't). So this means that gnulib's proposed
> iswwalpha(wwchar_t) function could be implemented using iswalpha()
> on Cygwin 1.7.x and will not cause the Unicode based tables to be
> included in the executable. This is good and nice.
I'm glad you see it that way.
> But if you say that the application should convert UTF-16 surrogates
> to UTF-32 before calling iswalpha: That's certainly a requirement
> for Cygwin 1.7.x application that want to support the entire Unicode
> character set. But it's outside of POSIX, and many GNU programs will
> not want to include this added complexity. Just try to apply this
> suggestion to gnulib's quotearg.c, then estimate the time someone
> would need to apply it also to regcomp.c, strftime.c, mbscasestr.c,
> coreutils/src/wc.c, and so on.
Cygwin's regcomp is taken from FreeBSD and is UTF-16 capable, including
surrogate handling. It only required two changes in the code.
But I see what you mean. Another layer which abstracts this problem
looks like the right thing to do.
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
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