[cfe-dev] [libc++] Conflict between "_UI" template parameter and Windows tchar.h macro

[Reid Kleckner via cfe-dev]

That is annoying, but it seems like something that we probably should work
around in libc++.

On Mon, May 29, 2017 at 7:45 PM, Orivej Desh via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> At present `algorithm' and `random' can not be included after `tchar.h' [1]
> because it contains
>
>      #define _UI     unsigned int
>
> and the former contain templates like
>
>      template <class _UI, _UI _Xp> struct __log2
>
> that fail to compile with
>
>      algorithm:2807: error C2332: 'class': missing tag name
>      algorithm:2807: error C2628: '<unnamed-tag>' followed by 'unsigned'
> is illegal (did you forget a ';'?)
>      algorithm:2807: error C2628: '<unnamed-tag>' followed by 'int' is
> illegal (did you forget a ';'?)
>      algorithm:2807: error C2993: '': illegal type for non-type template
> parameter '<unnamed-tag>'
>
> This affects compilation of open source libraries, in particular this
> BDB file [2] fails to compile because it includes tchar.h [3] before C++
> STL.  What is the best way to resolve this?  May libc++ rename or
> undefine `_UI'?
>
> [1] This one is from the old vc6 crt library, but Visual Studio 2017
>     installs crt with the same macros:
>     https://github.com/weolar/miniblink49/blob/f3ffb1ee/vc6/incl
> ude/crt/tchar.h#L838
> [2] https://github.com/berkeleydb/libdb/blob/master/lang/cxx/cxx_seq.cpp
> [3] https://github.com/berkeleydb/libdb/blob/master/src/dbinc/win_db.h#L33
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