c++ - Compile OpenMP programs with gcc compiler on OS X Yosemite

Question

$ gcc 12.c -fopenmp
12.c:9:9: fatal error: 'omp.h' file not found
#include<omp.h>
    ^
1 error generated.

While compiling openMP programs I get the above error. I am using OS X Yosemite. I first tried by installing native gcc compiler by typing gcc in terminal and later downloaded Xcode too still I got the same error. Then I downloaded gcc through:

$ brew install gcc

Still I'm getting the same error. I did try changing the compiler path too still it shows:

$ which gcc
/usr/bin/gcc

So how do I compile programs with gcc?

Answer 1

EDIT: As of 13 Aug 2017 the --without-multilib option is no longer present in Homebrew and should not be used. The standard installation

brew install gcc

will provide a gcc installation that can be used to compile OpenMP programs. As below it will be installed into /usr/local/bin as gcc-<version>. The current gcc version available from Homebrew (as of writing) will install as gcc-8. You can compile programs with OpenMP support using it via

gcc-8 -fopenmp hello.c

Alternatively you could put an alias in your .bashrcfile as

alias gcc='gcc-8'

and then compile using

gcc -fopenmp hello.c

---

Note: I'm leaving the original post here in case it is useful to somebody.

The standard gcc available on OS X through XCode and Clang doesn't support OpenMP. To install the Homebrew version of gcc with OpenMP support you need to install it with

brew install gcc --without-multilib

or as pointed out by @Mark Setchell

brew reinstall gcc --without-multilib

This will install it to the /usr/local/bin directory. Homebrew will install it as gcc-<version> so as not to clobber the gcc bundled with XCode.