Using the OpenMP* Libraries

This section describes the steps needed to set up and use the OpenMP* Libraries from the command line. On Windows* systems, you can also build applications compiled with the OpenMP libraries in the Microsoft Visual Studio* development environment.

For a summary of the support provided by the libraries provided with Intel compilers, see OpenMP* Source Compatibility and Interoperability with Other Compilers.

For a list of the options and libraries used by the OpenMP libraries, see OpenMP* Support Libraries.

Set up your environment for access to the Intel compiler to ensure that the appropriate OpenMP library is available during linking. On Windows systems, you can either execute the appropriate batch (.bat) file or use the command-line window supplied in the compiler program folder that already has the environment set up. On Linux and Mac OS systems, you can source the appropriate script file (iccvars file).

During compilation, ensure that the version of omp.h used when compiling is the version provided by that compiler. For example, on Linux systems when compiling with the GNU C/C++ compiler, use the omp.h provided with the GNU C/C++ compiler.

Caution

Be aware that when using the GNU*/Microsoft* compiler, you may inadvertently use inappropriate header/module files. To avoid this, copy the header/module file(s) to a separate directory and put it in the appropriate include path using the -I option.

If a program uses data structures or classes that contain members with data types defined in omp.h file, then source files that use those data structures should all be compiled with the same omp.h file.

The following table lists the commands used by the various command-line compilers for both C and C++ source files.:

Operating System	C Source Module	C++ Source Module
Linux*	GNU: gcc Intel: icc	GNU: g++ Intel: icpc
Mac OS* X	GNU: gcc Intel: icc	GNU: g++ Intel: icpc
Windows*	Visual C++: cl Intel: icl	Visual C++: cl Intel: icl

For information on the OpenMP libraries and options used by the Intel compiler, see OpenMP* Support Libraries.

Using Intel OpenMP* Libraries from Visual Studio*

When using systems running a Windows OS, you can make certain changes in the Visual C++ Visual Studio 2005 development environment to allow you to use the Intel C++ Compiler and Visual C++ to create applications that use the Intel OpenMP libraries.

Note

Microsoft Visual C++ must have the symbol _OPENMP_NOFORCE_MANIFEST defined or it will include the manifest for the vcomp90 dlls. While this may not appear to cause a problem on the build system, it will cause a problem when the application is moved to another system that does not have this DLL installed.

Set the project Property Pages to indicate the Intel OpenMP run-time library location:

Open the project's property pages in from the main menu: Project > Properties (or right click the Project name and select Properties) .
Select Configuration Properties > Linker > General > Additional Library Directories
Enter the path to the Intel compiler libraries. For example, for an IA-32 architecture system, enter:
```
<Intel_compiler_installation_path>\IA32\LIB
```

Make the Intel OpenMP dynamic run-time library accessible at run-time; you must specify the corresponding path:

Open the project's property pages in from the main menu: Project > Properties (or right click the Project name and select Properties).
Select Configuration Properties > Debugging > Environment
Enter the path to the Intel compiler libraries. For example, for an IA-32 architecture system, enter:
```
PATH=%PATH%;<Intel_compiler_installation_path>\IA32\Bin
```

Add the Intel OpenMP run-time library name to the linker options and exclude the default Microsoft OpenMP run-time library:

Open the project's property pages in from the main menu: Project > Properties (or right click the Project name and select Properties).
Select Configuration Properties > Linker > Command Line > Additional Options
Enter the OpenMP library name and the Visual C++ linker option, /nodefaultlib.

Command-Line Examples, Linux OS and Mac OS X

To compile and link (build) the entire application with one command using the Intel OpenMP libraries, specify the following Intel compiler command:

Type of File	Commands
C source	`icc -openmp hello.c`
C++ source	`icpc -openmp hello.cpp`

By default, the Intel compilers perform a dynamic link of the OpenMP libraries. To perform a static link (not recommended), add the option -openmp-link static. The Intel compiler option -openmp-link controls whether the linker uses static or dynamic OpenMP libraries on Linux OS and Mac OS X systems (default is -openmp-link dynamic).

You can also use both Intel C++ icc/icpc and GNU gcc/g++ compilers to compile parts of the application and create object files (object-level interoperability). In this example, the GNU compiler compiles the C file foo.c (the gcc option -fopenmp enables OpenMP support), and the Intel compiler links the application using the Intel OpenMP library:

Type of File	Commands
C source	`gcc -fopenmp -c foo.c` `icc -openmp foo.o`
C++ source	`g++ -fopenmp -c foo.cpp` `icpc -openmp foo.o`

Type of File

Commands

C source

gcc -fopenmp -c foo.c

icc -openmp foo.o

C++ source

g++ -fopenmp -c foo.cpp

icpc -openmp foo.o

When using GNU gcc or g++ compiler to link the application with the Intel compiler OpenMP compatibility library, you need to explicitly pass the Intel OpenMP library name using the -l option, the Linux pthread library using the -l option, and path to the Intel libraries where the Intel C++ compiler is installed using the -L option:

Type of File	Commands
C source	`gcc -fopenmp -c foo.c bar.c` `gcc foo.o bar.o -liomp5 -lpthread -L<icc_dir>/lib`

Type of File

Commands

C source

gcc -fopenmp -c foo.c bar.c

gcc foo.o bar.o -liomp5 -lpthread -L<icc_dir>/lib

You can mix object files, but it is easier to use the Intel compiler to link the application so you do not need to specify the gcc -l option, -L option, and the -lpthread option:

Type of File	Commands
C source	`gcc -fopenmp -c foo.c` `icc -openmp -c bar.c` `icc -openmp foo.o bar.o`

Type of File

Commands

C source

gcc -fopenmp -c foo.c

icc -openmp -c bar.c

icc -openmp foo.o bar.o

You can mix OpenMP object files compiled with the GNU gcc compiler, the Intel® C++ Compiler, and the Intel® Fortran Compiler.

Note

You cannot mix object files compiled by the Intel Fortran compiler and the gfortran compiler.

The table illustrates examples of using the Intel Fortran compiler or the GNU Fortran compiler to link all the objects:

Type of File	Commands
Mixed C and Fortran sources	`ifort -openmp -c foo.f` `icc -openmp -c ibar.c` `gcc -fopenmp -c gbar.c` `ifort -openmp foo.o ibar.o gbar.o`

Type of File

Commands

Mixed C and Fortran sources

ifort -openmp -c foo.f

icc -openmp -c ibar.c

gcc -fopenmp -c gbar.c

ifort -openmp foo.o ibar.o gbar.o

Type of File	Commands
Mixed C and GNU Fortran sources	`gfortran -fopenmp -c foo.f` `icc -openmp -c ibar.c` `gcc -fopenmp -c gbar.c` `gfortran foo.o ibar.o gbar.o -lirc -liomp5 -lpthread -lc -L<icc_dir>/lib`

Type of File

Commands

Mixed C and GNU Fortran sources

gfortran -fopenmp -c foo.f

icc -openmp -c ibar.c

gcc -fopenmp -c gbar.c

gfortran foo.o ibar.o gbar.o -lirc -liomp5 -lpthread -lc -L<icc_dir>/lib

Alternatively, you could use the Intel compiler to link the application, but need to pass multiple gfortran libraries using the -l options on the link line:

Type of File	Commands
Mixed C and Fortran sources	`gfortran -fopenmp -c foo.f` `icc -openmp -c ibar.c` `icc -openmp foo.o bar.o -lgfortranbegin -lgfortran`

Type of File

Commands

Mixed C and Fortran sources

gfortran -fopenmp -c foo.f

icc -openmp -c ibar.c

icc -openmp foo.o bar.o -lgfortranbegin -lgfortran