So I tried to add my first linux regression runner using libc++ with clang, and I'm seeing the following error saying it can't find <cstddef>: http://www.boost.org/development/tests/develop/developer/output/teeks99-02-d... "clang++-3.9" -c -x c++ -Wno-c99-extensions -std=c++1z -stdlib=libc++ -O0 -g -fno-inline -Wall -g -m64 -DBOOST_ALL_NO_LIB=1 -DBOOST_CHRONO_STATIC_LINK=1 -DBOOST_CHRONO_THREAD_DISABLED -DBOOST_SYSTEM_NO_DEPRECATED -DBOOST_SYSTEM_STATIC_LINK=1 -DBOOST_TEST_NO_AUTO_LINK=1 -DBOOST_TIMER_STATIC_LINK=1 -I".." -o "/var/boost/run/results/boost/bin.v2/libs/accumulators/test/count.test/clang-linux-3.9~c++1z~lc/debug/link-static/count.o" "../libs/accumulators/test/count.cpp" In file included from ../libs/accumulators/test/count.cpp:6: In file included from ../boost/test/unit_test.hpp:18: In file included from ../boost/test/test_tools.hpp:17: In file included from ../boost/config.hpp:44: ../boost/config/select_stdlib_config.hpp:18:12: fatal error: 'cstddef' file not found # include <cstddef> ^ 1 error generated. However when I try to compile the following program on the same docker image (teeks99/boost-build:clang-3.9) // basic.cpp #include <cstddef> int main(int argc, char* argv[]) { size_t three = 3; return three; } with: $ clang++-3.9 -stdlib=libc++ -std=c++1z basic.cpp It works fine $ ./a.out $ echo $? 3 I can build this sample file fine with the whole command line shown above, so it doesn't seem to be one of the other options conflicting. Any thoughts on why boost code wouldn't be able to find this but some basic stuff would? One relevant detail, I'm building with clang 3.9, however the libc++ version that I'm using (ubuntu default) is the one that shipped with clang 3.7. That shouldn't preclude including a file! I also found a couple old threads with the same error, but never any good resolution. http://lists.boost.org/boost-testing/2012/07/7075.php http://lists.boost.org/boost-users/2012/11/76659.php Tom