Re: [boost] [config] gcc-4.8 and __GXX_EXPERIMENTAL_CXX0X__

Subject: Re: [boost] [config] gcc-4.8 and __GXX_EXPERIMENTAL_CXX0X__
From: Jonathan Wakely (jwakely.boost_at_[hidden])
Date: 2013-04-01 11:12:49

On 1 April 2013 15:58, Vicente J. Botet Escriba wrote:
> Le 01/04/13 16:35, Jonathan Wakely a écrit :
>
>> On 1 April 2013 15:17, Vicente J. Botet Escriba wrote:
>>>
>>> Hi,
>>>
>>> it seems that gcc-4.8 doesn't defines any more __GXX_EXPERIMENTAL_CXX0X__
>>> when the flag -std=c++11 is given.
>>
>> Are you sure?
>
> Maybe my installation is not correct, but with it __GXX_EXPERIMENTAL_CXX0X__
> is not defined. Could some check it?

I see it still defined with GCC 4.8 or 4.9

> BTW, there are some pages pointing to this problem on the net.
>
>> The standard library no longer checks it, using __cplusplus >= 201103L
>> instead, but the compiler still defines the old macro. The old macro
>> is still documented as being defined.
>
> Maybe there is a bug on gcc-4.8 ;-)
>
>>
>>> This means that all the BOOST_NO_CXX11_ are defined.
>>>
>>> Could something be done to make usable gcc-4.8 in c++11 mode?
>>
>> You could check the value of __cplusplus instead, because
>> __GXX_EXPERIMENTAL_CXX0X__ will stop being defined at some point
>> eventually.
>
> I'm not using it directly, but via boost/config.hpp
>
>>
>> A related topic I've been meaning to raise is that
>> <boost/config/stdlib/libstdcpp3.hpp> unconditionally defines:
>>
>> //  C++0x headers not yet (fully!) implemented
>> //
>> #  define BOOST_NO_CXX11_HDR_THREAD
>>
>> This is incorrect. Depending on how GCC was configured libstdc++ has
>> provided a complete <thread> since at least version 4.4, and for GCC
>> 4.8 it unconditionally provides a complete <thread>.
>>
>> This should be correct:
>>
>> #if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4)
>> #  define BOOST_NO_CXX11_HDR_THREAD
>> #elif (__GNUC__ == 4 && __GNUC_MINOR__ < 8)
>> # if !(defined(_GLIBCXX_HAS_GTHREADS) &&
>> defined(_GLIBCXX_USE_C99_STDINT_TR1) &&
>> defined(_GLIBCXX_USE_SCHED_YIELD) && defined(_GLIBCXX_USE_NANOSLEEP)
>> && defined(__GXX_EXPERIMENTAL_CXX0X__))
>> #  define BOOST_NO_CXX11_HDR_THREAD
>> #elif __cplusplus < 201103L
>> #  define BOOST_NO_CXX11_HDR_THREAD
>> #endif
>>
>>
> I don't know if some documentation needs to be updated, but if you have
> check it, could you to commit it?

I haven't checked it, and I don't have commit rights.

I'll run the tests and report back ...