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Date: Thu, 15 Nov 2012 12:53:40 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Subject: Re: type of wchar_t
* Yuri Kozlov <yuray@...yakino.ru> [2012-11-15 13:09:50 +0400]:
>
> arch/x86_64/bits/alltypes.h.sh
> #ifndef __cplusplus
> TYPEDEF int wchar_t;
> #endif
>
>
> arch/i386/bits/alltypes.h.sh
> #ifndef __cplusplus
> #ifdef __WCHAR_TYPE__
> TYPEDEF __WCHAR_TYPE__ wchar_t;
> #else
> TYPEDEF long wchar_t;
> #endif
> #endif
>
> (__WCHAR_TYPE__ is not defined everyware, so TYPEDEF long wchar_t;)
>
> arch/arm/bits/alltypes.h.sh
> #ifndef __cplusplus
> TYPEDEF unsigned wchar_t;
> #endif
>
>
> Why type of wchar_t is so differs?
>
because wchar_t is a broken concept and platform
abis and compilers have gratitous incompatibilities
you cannot have arbitrary definition because the L'x'
character constant and L"" string literal has a given
type in the compiler and you should use the same in
the wchar_t typedef
(different int types are not compatible, they can be
converted if the range is ok, but eg. calling function
through incompatible function pointer type is
undeinfed behaviour)
in c++ wchar_t is a keyword because otherwise
polimorphism and strict type checking of int vs
wchar_t would not work
(wchar_t must be distinct from any other int type)
in c99 the compiler could be loose and allow pointer to
any sufficiently aligned+sized+signed integer type
to work with L"", so eg. wchar_t could be long or int
as well on a 32bit platform
c11 has generics (implemented in the compiler) so the
compiler must have a type internally for L'' or L""[0]
and wchar_t must be defined as that type
so we either use the __WCHAR_TYPE__ defined by the
compiler (when it's defined), or use the abi specs
(which gives the align+size+sign information and
hopefully compilers agree on a single int type when
there are multiple choices)
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