Re: [Boost-build] [requires] cxx11_variadic_macros

Subject: Re: [Boost-build] [requires] cxx11_variadic_macros
From: Jürgen Hunold (jhunold_at_[hidden])
Date: 2015-10-14 01:12:27

Hi Raffi, 

Am Dienstag, 13. Oktober 2015, 19:45:05 schrieb Edward Diener:
> On 10/13/2015 11:41 AM, Raffi Enficiaud wrote:
> > Hi all,
> > 
> > I have the following requirement on my bjam:
> > 
> > requirements_boost_test = [ requires cxx11_variadic_macros ] ;

On which Jamfile? Can you either attach a small testcase or point us to the 
feature branch containing the original Jamfile?
 
> > When I compile it on clang/OSX, in C++03 mode, I have this:
> > 
> > ../../../b2
> > 
> >      - Boost.Config Feature Check: cxx11_variadic_macros : yes
> >      - Boost.Config Feature Check: cxx11_decltype : no
> >      - Boost.Config Feature Check: cxx11_hdr_random : yes
> >      - Boost.Config Feature Check: cxx11_hdr_tuple : no
> >      - Boost.Config Feature Check: cxx11_hdr_initializer_list : no

So either clang enables c++11 variadic macros in c++03 mode (which I doubt) or 
your test detects C99 variadic macros, too..

> > When I compile it on clang6/OSX, in C++11 mode, I have this
> > 
> > ../../../b2  cxxflags="-stdlib=libc++ -std=c++11"
> > linkflags="-stdlib=libc++"
> > 
> >      - Boost.Config Feature Check: cxx11_variadic_macros : yes
> >      - Boost.Config Feature Check: cxx11_decltype : yes
> >      - Boost.Config Feature Check: cxx11_hdr_random : yes
> >      - Boost.Config Feature Check: cxx11_hdr_tuple : yes
> >      - Boost.Config Feature Check: cxx11_hdr_initializer_list : yes
> > 
> > The cxx11_variadic_macros is active for both configuration, but the
> > variadic macros are not available with the "b2" toolset configuration.
> 
> What exactly do you mean when you say 'the
> variadic macros are not available with the "b2" toolset configuration' ?

C++11 variadic macros should not be enabled with "-std=c++03". The question is 
if the detection report "true" if only C99 variadic macros are available.

> Variadic macro support in Boost PP ( and Boost VMD ), and libraries
> which use Boost PP, is not determined by Boost config. Instead it is
> determined internally based on the compiler and/or level of c++11
> support. In general compiling with c++11 support will turn on variadic
> macro support in Boost PP for most compilers, but both VC++ 8 on up and
> clang have variadic macro support turned on automatically in Boost PP.
> You can also force variadic macro support in Boost PP by defining
> BOOST_PP_VARIADICS to 1.
> 
> Of course if you are not talking about variadic macros in Boost PP the
> preceding paragraph does not help you.

No, I guess it is about variadic macros in Boost.Test and selective activating 
the test for them only if c++11 is enabled.

> > When it says cxx11_variadic_macros, I believe it does not try to compile
> > with C++11 mode.
> > 
> > How would I detect properly the support for variadic macros?

You are on the correct path. It is hard to say more without looking at or 
trying you test cases. And I have to figure out how to get b2 to spit out the 
generated command lines for the configuration tests...

Yours,

Jürgen
-- 
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