Compile OpenMP programs with gcc compiler on OS X Yosemite

osx_openmp_gcc.txt

https://en.wikipedia.org/wiki/OpenMP
https://stackoverflow.com/questions/29057437/compile-openmp-programs-with-gcc-compiler-on-os-x-yosemite
https://stackoverflow.com/questions/30049486/what-does-gcc-without-multilib-mean

# reinstall gcc with --without-multilib
brew update
time brew reinstall gcc --without-multilib
real	41m52.433s
user	121m53.094s
sys	32m39.945s

# check brew install 
ls /usr/local/bin/gcc*
/usr/local/bin/gcc-7		/usr/local/bin/gcc-nm-7
/usr/local/bin/gcc-ar-7		/usr/local/bin/gcc-ranlib-7

# create an alias at ~/.bash_profile
alias gcc='gcc-7'
source ~/.bash_profile

cat<<EOF > hello.c 
#include <stdio.h>

int main(void)
{
    #pragma omp parallel
    printf("Hello, world.\n");
    return 0;
}
EOF

# compile with flag -fopenmp
gcc -fopenmp hello.c -o hello

# execute hello
./hello
Hello, world.
Hello, world.
Hello, world.
Hello, world.
Hello, world.
Hello, world.
Hello, world.
Hello, world.