Re: [boost] [build] How to use with clang on windows?

Subject: Re: [boost] [build] How to use with clang on windows?
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2016-03-27 18:15:52

On 26 Mar 2016 at 6:52, Edward Diener wrote:

> The clang build which targets VC++ on Windows, as opposed to the clang 
> build which targets mingw(-64)/gcc on Windows, 'emulates' the 
> non-standard VC++ preprocessor so it can compile Windows API headers and 
> VC++ header files. Exactly what VC++ preprocessor 'bugs' it emulates and 
> how successful this emulation is I do not know, but I know it is done 
> because I was told of it in the clang developer forum and I encountered 
> a clang targeting VC++ preprocessor 'bug' which was explained to me as 
> an emulation of VC++.

As of VS2015 Update 2 RC, the MSVCRT, STL and Windows SDK headers 
supplied no longer require clang to act in MSVC compatibility mode to 
compile. I am compiling AFIO v2 for windows using LLVM clang with 
these options:

clang.exe -fpic "stdafx.h" -fmsc-version="1900" -std=c++1y "x64\Debug 
clang\" -Wall -fstrict-aliasing -I "../include" -g2 -gdwarf-2 -O0 -x 
c++-header -U "__STDC__" -D "WIN32" -D "_DEBUG" -D "_WINDOWS" -D 
"_USRDLL" -D "BOOST_AFIO_EXPORTS" -D "_UNICODE" -D "UNICODE" -D 
"UNICODE=1" -D "_UNICODE=1" -D "AFIO_STANDALONE=1" -frtti 
-fno-omit-frame-pointer -fno-ms-compatibility -fexceptions -o 
"x64\Debug clang\%(filename).obj" -fms-extensions -fno-short-enums 

The key improvement with VS2015 Update 2 is the -fno-ms-compatibility 
is now possible even when using the Dinkumware STL, the Parallel 
Patterns Library or the Windows SDK. This means that clang treats 
your code as strictly as normal, and it is *very* useful for linting 
your code (the complete C++ 14 language support is also very handy).

Note that I cannot get MSVCRT-as-a-dll working with this 
configuration, for that you still need -fms-compatibility. 
MSVCRT-as-a-static-library is working. I assuming this is a RC 
related problem which will be fixed soon, the cause is the char16_t 
and char32_t support misdetection.

I am not using any preprocessor tricks which are incompatible with 
MSVC, so I cannot say if the broken preprocessor emulation is still 
present with -fno-ms-compatibility. I would suspect not. 
-fms-extensions are things like declspec markup support, I am not 
aware of it changing any parsing behaviour.

Niall

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