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Re: Fix u32toutf8 so it encodes values > 0xFFFF correctly.


From: Eric Blake
Subject: Re: Fix u32toutf8 so it encodes values > 0xFFFF correctly.
Date: Wed, 22 Feb 2012 15:32:29 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.1) Gecko/20120209 Thunderbird/10.0.1

On 02/22/2012 03:01 PM, Linda Walsh wrote:
>     My question had to do with an unqualified wint_t not
> unsigned wint_t and what platform existed where an 'int' type or
> wide-int_t, was, without qualifiers, unsigned.  I still would like
> to know -- and posix allows int/wide-ints to be unsigned without
> the unsigned keyword?

'int' is signed, and at least 16 bits (these days, it's usually 32).  It
can also be written 'signed int'.

'unsigned int' is unsigned, and at least 16 bits (these days, it's
usually 32).

'wchar_t' is an arbitrary integral type, either signed or unsigned, and
capable of holding the value of all valid wide characters.   It is
possible to define a system where wchar_t and char are identical
(limiting yourself to 256 valid characters), but that is not done in
practice.  More common are platforms that use 65536 characters (only the
basic plane of Unicode) for 16 bits, or full Unicode (0 to 0x10ffff) for
32 bits.  Platforms that use 65536 characters and 16-bit wchar_t must
have wchar_t be unsigned; whereas platforms that have wchar_t wider than
the largest valid character can choose signed or unsigned with no impact.

'wint_t' is an arbitrary integral type, either signed or unsigned, at
least as wide as wchar_t, and capable of holding the value of all valid
wide characters and the sentinel WEOF.  Like wchar_t, it may hold values
that are neither WEOF or valid characters; and in fact, it is more
likely to do so, since either wchar_t is saturated (all bit values are
valid characters) and thus wint_t is a wider type, or wchar_t is sparse
(as is the case with 32-bit wchar_t encoding Unicode), and the addition
of WEOF to the set does not plug in the remaining sparse values; but
using such values has unspecified results on any interface that takes a
wint_t.  WEOF only has to be distinct, it does not have to be negative.

Don't think of it as 'wide-int', rather, think of it as 'the integral
type that both contains wchar_t and WEOF'.  You cannot write 'signed
wint_t' nor 'unsigned 'wint_t'.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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