See http://blogs.msdn.com/b/vcblog/archive/2015/12/04/introducing-clang-with-mic... I tried building the Boost.Filesystem DLL with clang/c2 using the Visual Studio solution from libs/filesystem/test/msvc. As indicated the blog post, the following changes were needed in the project's properties: Configuration Properties General Platform Toolset : Clang 3.7 with Microsoft CodeGen (v140_clang_3_7) C/C++ General Warning Level : EnableAllWarnings (-Wall) Code Generation Enable C++ Exceptions: Yes (-fexceptions) Language Enable Run-Time Type Information: Yes (-frtti) Precompiled Headers Precompiled Header: Not using Precompiled Headers The operations.cpp compile failed with the following errors: 2> operations.cpp 2> In file included from ..\..\..\src\operations.cpp:44: 2> In file included from ../../../../..\boost/filesystem/operations.hpp:25: 2> In file included from ../../../../..\boost/filesystem/path.hpp:29: 2> In file included from ../../../../..\boost/shared_ptr.hpp:17: 2> In file included from ../../../../..\boost/smart_ptr/shared_ptr.hpp:28: 2> In file included from ../../../../..\boost/smart_ptr/detail/shared_count.hpp:29: 2> In file included from ../../../../..\boost/smart_ptr/detail/sp_counted_base.hpp:45: 2>../../../../..\boost/smart_ptr/detail/sp_counted_base_clang.hpp(29,1): error : cannot mangle this C11 atomic type yet 2> inline void atomic_increment( atomic_int_least32_t * pw ) 2> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 2>../../../../..\boost/smart_ptr/detail/sp_counted_base_clang.hpp(34,1): error : cannot mangle this C11 atomic type yet 2> inline boost::int_least32_t atomic_decrement( atomic_int_least32_t * pw ) 2> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 2>../../../../..\boost/smart_ptr/detail/sp_counted_base_clang.hpp(39,1): error : cannot mangle this C11 atomic type yet 2> inline boost::int_least32_t atomic_conditional_increment( atomic_int_least32_t * pw ) 2> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ So it looks like the clang/c2 toolset doesn't support atomics yet. The __c2__ and __c2_version__ macros allow detection of the clang/c2 toolset, could a workaround be added to shared_ptr? I know we don't usually worry about workarounds for preview (i.e. early beta) compiler releases, but the ability to add the clang/c2 toolset to local tests for library developers working on Windows will be a big plus IMO. --Beman PS: Has anyone figured out how to invoke clang/c2 from the command line?