Is C++ compilable with OpenMP and boost on MacOS?

Question

I have tried many things now and have come to some conclusions. Maybe, I oversee something but it seems that I cannot accomplish what I desire.

The question is: Is there any possibility to compile C++ on MacOS High Sierra with OpenMP and boost?

Some findings (correct me if I am wrong):

• OpenMP is supported by Clang BUT not by the standard MacOS-clang compiler delivered with MacOS which is ALSO the only compiler XCode9 supports
• g++ supports OpenMP
• If I install Boost via homebrew, then it will use the clang compiler (which cannot be changed easily), so that libc++ will be used
• g++ uses libstdc++ by default which is not easy to change

As a consequence, it seems that I cannot have both... OpenMP is only supported if I use gcc. But gcc uses libstdc++ instead of libc++, so that I get linker errors if I try to link against boost installed via homebrew with libc++.

Is there any chance to get both OpenMP and and boost running?

PS: Please don't link to some >1 year old threads, XCode8 is another story (earlier XCode versions support different compilers) and clang-omp would be another story (it is no longer supported).

Answer 1

Standard Apple's clang supports OpenMP. They just disabled the driver option. But you can use the frontend option instead this way: clang -Xclang -fopenmp <you_program> -L <path to libomp.a> -lomp

Also, you need to set DYLD_LIBRARY_PATH environmental variable: export DYLD_LIBRARY_PATH=<path to libomp.dylib>

Answer 2

Since you mentioned in passing brew install clang-omp, it's been merged into brew install llvm. That's really a very useful choice if you are willing to do it, since you get llvm 5 and C++17 if you need it. It's fully OpenMP compatible using the standard options (ie, -fopenmp).

You can also try my brew formula to use the built-in clang, but you'd still need to set up custom options as in Alexey Bataev's answer. Install with brew:

brew install cliutils/apple/libomp

This only adds the openMP dynamic library and header, nothing else. Then build with:

clang++ -Xpreprocessor -fopenmp -lomp <other arguments...>

See the readme. If you are using cmake, the helper file here might help.