sap sap - 1 month ago 84
C++ Question

Using OpenMP with C++11 on Mac OS

I am trying to use some OpenMP multithreading features in my C++11 code like:

#pragma omp parallel for


When I try to compile using:

clang++ -std=c++11 -stdlib=libc++ -fopenmp main.cpp -o main.o


I get the below error:

clang: error: unsupported option '-fopenmp'


I alternatively tried compiling using:

g++ -fopenmp main.cpp -o main.o


But this gives the exact same error.

Would appreciate very much if you could advise how can I compile C++11 code that has OpenMP features on Mac OS 10.12. The other questions on posts here and elsewhere explain compiling C code for OpenMP, however, I couldn't find anything for C++11.

I get an error when I try to install libiomp, I get errors:

$ brew install libiomp
==> Auto-updated Homebrew!
Updated 1 tap (homebrew/core).
==> Updated Formulae
ansible-cmdb djview4 khard oysttyer shyaml yazpp
asciinema2gif doctl macvim pazpar2 vala you-get
avro-c elixir mailhog python vdirsyncer youtube-dl
bash-git-prompt file-roller meson python3 vim
commandbox glib metaproxy rtv x265
consul-backinator gtkextra offlineimap s-search xonsh

Error: Could not link:
/usr/local/share/doc/homebrew

Please delete these paths and run `brew update`.
Error: Could not link:
/usr/local/share/man/man1/brew.1

Please delete these paths and run `brew update`.
Error: No available formula with the name "libiomp"
==> Searching for similarly named formulae...
Error: No similarly named formulae found.
==> Searching taps...
Error: No formulae found in taps.


If I run using g++-6, based on Mark Setchell's post below, it works fine, thanks, I however get the below warnings, would appreciate any suggestions on how to avoid these:

$ /usr/local/bin/g++-6 -std=c++11 -fopenmp main.cpp -o main.o
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:4:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:4:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:89:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:89:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:551:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:551:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:1432:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:1432:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:1799:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:1799:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:1995:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:1995:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2033:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2033:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2425:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2425:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2559:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2559:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2597:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2597:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2672:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2672:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2837:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2837:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2962:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:2962:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3139:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3139:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3442:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3442:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3588:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3588:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3630:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:3630:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:5253:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:5253:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:5452:11: warning: section "__textcoal_nt" is deprecated
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~
/var/folders/jr/30r6h4cj4tl48q_cg9bt5f5h0000gn/T//ccq73Zfg.s:5452:11: note: change section name to "__text"
.section __TEXT,__textcoal_nt,coalesced,pure_instructions
^ ~~~~~~~~~~~~~

Answer

If you want to compile C++11 OpenMP code on OSX, the easiest way is to use gcc which you can install via homebrew.

First, check the available options:

brew options gcc

Sample Output

--with-all-languages
    Enable all compilers and languages, except Ada
--with-java
    Build the gcj compiler
--with-jit
    Build the jit compiler
--with-nls
    Build with native language support (localization)
--without-fortran
    Build without the gfortran compiler
--without-multilib
    Build without multilib support
--HEAD
    Install HEAD version

So, I suspect you want:

brew install gcc --without-multilib --without-fortran

Once you have got it installed, you need to make sure you are using the homebrew version rather than the one Apple supplies. You need to know that homebrew installs everything in /usr/local/bin and that the C++ compiler is g++-6. So, you either need to compile with:

/usr/local/bin/g++-6 -std=c++11 -fopenmp main.cpp -o main

or, set up your PATH in your login profile:

export PATH=/usr/local/bin:$PATH

then you can just do:

g++-6 -std=c++11 -fopenmp ...

Note that if you choose the second option above (i.e. the export PATH=... option), you will either need to also type the export command in your current session once to activate it, or log out and log back in since your profile commands are only executed on login.

AFAIK, there is no need to explicitly install libiomp - not sure why you did that.

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