Compiling OpenMP Programs

All compilers installed on Brown include OpenMP functionality for C, C++, and Fortran. An OpenMP program is a single process that takes advantage of a multi-core processor and its shared memory to achieve a form of parallel computing called multithreading. It distributes the work of a process over processor cores in a single compute node without the need for MPI communications.

OpenMP programs require including a header file:

Language	Header Files
Fortran 77	INCLUDE 'omp_lib.h'
Fortran 90	use omp_lib
Fortran 95	use omp_lib
C	#include <omp.h>
C++	#include <omp.h>

Sample programs illustrate task parallelism of OpenMP:

• omp_hello.f
• omp_hello.f90
• omp_hello.f95
• omp_hello.c
• omp_hello.cpp

A sample program illustrates loop-level (data) parallelism of OpenMP:

• omp_loop.c

To load a compiler, enter one of the following:

$ module load intel
$ module load gcc

The following table illustrates how to compile your shared-memory program. Any compiler flags accepted by ifort/icc compilers are compatible with OpenMP:

Language	Intel Compiler	GNU Compiler
Fortran 77	$ ifx -qopenmp myprogram.f -o myprogram	$ gfortran -fopenmp myprogram.f -o myprogram
Fortran 90	$ ifx -qopenmp myprogram.f90 -o myprogram	$ gfortran -fopenmp myprogram.f90 -o myprogram
Fortran 95	$ ifx -qopenmp myprogram.f95 -o myprogram	$ gfortran -fopenmp myprogram.f95 -o myprogram
C	$ icx -qopenmp myprogram.c -o myprogram	$ gcc -fopenmp myprogram.c -o myprogram
C++	$ icpx -qopenmp myprogram.cpp -o myprogram	$ g++ -fopenmp myprogram.cpp -o myprogram

The Intel and GNU compilers will not output anything for a successful compilation. Also, the Intel compiler does not recognize the suffix .f95.

Here is some more documentation from other sources on OpenMP:

• OpenMP Home
• Community of OpenMP Users
• Intel OpenMP
• GCC OpenMP

Back to the Compiling Programs section