chrono does not compile with clang from XCode 4.5.2 with -std=c++11 -stdlib=libc++ and -arch armv7

[Franz Detro <franz.detro@…>]

When trying to compile chrono with the Xcode 4.5.2 clang compiler on MacOS X for iOS with

-std=c++11 -stdlib=libc++ and -arch armv7

one gets compile errors. Compile log attached.

I'm using the following configuration and everything is right.

using clang : 3.2 : /Users/viboes/clang/clang+llvm-3.2-x86_64-apple-darwin11/bin/clang++ ;
using clang : 3.2xl : /Users/viboes/clang/clang+llvm-3.2-x86_64-apple-darwin11/bin/clang++ : <cxxflags>"-std=c++11 -stdlib=libc++" <linkflags>"-std=c++11 -stdlib=libc++" ;

[viboes]

The error appears when the standard library doesn't uses constexpr for max()

41	./boost/chrono/duration.hpp:353:49: error: constexpr function never produces a constant expression
42	        static BOOST_CHRONO_LIB_CONSTEXPR float lowest() BOOST_CHRONO_LIB_NOEXCEPT_OR_THROW
43	                                                ^
44	./boost/chrono/duration.hpp:355:21: note: non-constexpr function 'max' cannot be used in a constant expression
45	            return -(std::numeric_limits<float>::max) ();
46	                    ^

BOOST_CHRONO_LIB_CONSTEXPR is defined as follows

#if defined( BOOST_NO_CXX11_NUMERIC_LIMITS )
#define BOOST_CHRONO_LIB_CONSTEXPR
#elif defined(_LIBCPP_VERSION) && _LIBCPP_VERSION < 1002
  #define BOOST_CHRONO_LIB_CONSTEXPR
#else
  #define BOOST_CHRONO_LIB_CONSTEXPR BOOST_CONSTEXPR
#endif

Could you tell me what is the value of BOOST_NO_CXX11_NUMERIC_LIMITS and _LIBCPP_VERSION on the environment you get the error?

[Franz Detro <franz.detro@…>]

BOOST_NO_CXX11_NUMERIC_LIMITS is undefined.

Here's the extract of clangs config file:

#define _LIBCPP_VERSION 1101

#define _LIBCPP_ABI_VERSION 1

The problem is related to the combination of -std=c++11 and -stdlib=libc++. If I use only one of them, everything is fine.

[Marshall Clow]

This was fixed (by Apple) as part of the Xcode 4.6 release.

Specifically, std::numeric_limits<>::max() is now constexpr.

[viboes]

Replying to Franz Detro <franz.detro@…>:

BOOST_NO_CXX11_NUMERIC_LIMITS is undefined.

Here's the extract of clangs config file:

#define _LIBCPP_VERSION 1101

#define _LIBCPP_ABI_VERSION 1

The problem is related to the combination of -std=c++11 and -stdlib=libc++. If I use only one of them, everything is fine.

Please could you try the following patch

#if defined( BOOST_NO_CXX11_NUMERIC_LIMITS )
#define BOOST_CHRONO_LIB_CONSTEXPR
#elif defined(_LIBCPP_VERSION) && _LIBCPP_VERSION <= 1101
  #define BOOST_CHRONO_LIB_CONSTEXPR
#else
  #define BOOST_CHRONO_LIB_CONSTEXPR BOOST_CONSTEXPR
#endif

[viboes]

Replying to marshall:

This was fixed (by Apple) as part of the Xcode 4.6 release.

Specifically, std::numeric_limits<>::max() is now constexpr.

Do you know since which _LIBCPP_VERSION this is fixed?

[Marshall Clow]

_LIBCPP_VERSION was changed to 1101 soon after std::numeric_limits<>::max() was marked as constexpr.

You can check for that, or use #ifdef _LIBCPP_CONSTEXPR which was added at the same time as the change.

[viboes]

Thanks for the info. Committed revision [83842].

[viboes]

(In [83866]) Chrono: merge to fix #8367.