clang++ via homebrew (llvm38) - compile error with system includes

Question

I'm using a Mac for development with 10.11.3

Due to Apple llvm in Xcode 7 still not supporting openmp, I have used homebrew to install a more up to date llvm/clang that does support openmp via:

$ brew tap homebrew/versions
$ brew install llvm38

I then have a very simple C++ test program, which is more or less a standard openmp test and which I know should compile:

#include <iostream>
#include <omp.h>

int main(void)
{
    #pragma omp parallel for
    for( unsigned v = 0; v < 15; ++v )
    {
        printf("thread %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
    }
}

Installing with homebrew, it suggests that you need to specify a few extra things to successfully compile, in particular, the path to the c++ system headers that were installed from the llvm38 package. This leads me to the following command line:

/usr/local/opt/llvm38/bin/clang++-3.8 -fopenmp openmp.cpp -stdlib=libc++ -nostdinc++ -I /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/ -L/usr/local/opt/llvm38/lib/llvm-3.8/lib

However, upon running this command, the compilation fails:

machine:tests me$ /usr/local/opt/llvm38/bin/clang++-3.8 openmp.cpp -stdlib=libc++ -nostdinc++ -I /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/ -L/usr/local/opt/llvm38/lib/llvm-3.8/lib
In file included from openmp.cpp:1:
In file included from /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/iostream:38:
In file included from /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/ios:215:
In file included from /usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/iosfwd:90:
/usr/local/opt/llvm38/lib/llvm-3.8/include/c++/v1/wchar.h:119:15: fatal error: 'wchar.h' file not found
#include_next <wchar.h>
              ^
1 error generated.

Does anyone know how to resolve this problem and get a successful compile?

yes, sorry -fopenmp is important to compile with openmp, but that is not the cause of this error. cheers. — Murray Evans, May 19 '16 at 15:38
Have you installed the Xcode Command Line Tools? And reinstalled them since any OS upgrades? http://stackoverflow.com/a/32338889/2836621 — Mark Setchell, May 19 '16 at 15:49
That has made the difference. Why would that make a difference? (Had previously installed but presumably there has been an OS update). — Murray Evans, May 19 '16 at 15:58
The OpenMP clang relies on standard header files being available from your standard compiler. — Mark Setchell, May 19 '16 at 16:10
I understand that, just don't understand why they were not already there if XCode and command line tools had been previously installed. Still, thanks for the help. — Murray Evans, May 19 '16 at 16:22

score 4 · Answer 1 · answered May 19 '16 at 16:00

4

As per the comment on the original question, reinstalling/updating Xcode developer tools solved the issue.

xcode-select --install

answered May 19 '16 at 16:00

Murray Evans

81
5

clang++ via homebrew (llvm38) - compile error with system includes

1 Answers1