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

Set up your environment for access to the Intel® C++ 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 macOS* systems, you can source the appropriate script file (compilervars file).

During compilation, ensure that the version of omp.h used when compiling is the version provided by that compiler. For example, use the omp.h provided with GCC* when you compile on Linux systems.

### CAUTION

Be aware that when using the GCC or 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 | gcc Intel: icc | g++ Intel: icpc
macOS* [prior to v10.9] | gcc Intel: icc | g++ Intel: icpc
macOS* [v10.9 and later] | clang Intel: icc | clang++ Intel: or icpc
Windows | Visual C++*: cl Intel: icl | Visual C++: cl Intel: icl

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

## Command-Line Examples, Windows

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

Type of File | Commands
--- | ---
C source, dynamic link | `icl /MD /Qopenmp hello.c`
C++ source, dynamic link | `icl /MD /Qopenmp hello.cpp`

When using the Microsoft Visual C++ Compiler, you should link with the Intel® OpenMP compatibility library. You need to avoid linking the Microsoft OpenMP run-time library (vcomp) and explicitly pass the name of the Intel® OpenMP compatibility library as linker options (following /link):

Type of File | Commands
--- | ---
C source, dynamic link | `cl /MD /openmp hello.c /link /nodefaultlib:vcomp libiomp5md.lib`
C++ source, dynamic link | `cl /MD /openmp hello.cpp /link /nodefaultlib:vcomp libiomp5md.lib`

You can also use the Intel C++ Compiler with the Visual C++ Compiler to compile parts of the application and create object files (object-level interoperability). In this example, the Intel C++ Compiler compiles and links the entire application:

Type of File | Commands
--- | ---
C source, dynamic link | `cl /MD /openmp /c f1.c f2.c` `icl /MD /Qopenmp /c f3.c f4.c` `icl /MD /Qopenmp f1.obj f2.obj f3.obj f4.obj /Feapp /link /nodefaultlib:vcomp`

The first command produces two object files compiled by Visual C++ Compiler, and the second command produces two more object files compiled by the Intel C++ Compiler. The final command links all four object files into an application.

Alternatively, the third line below uses the Visual C++ linker to link the application and specifies the Compatibility library libiomp5md.lib at the end of the third command:

Type of File | Commands
--- | ---
C source, dynamic link | `cl /MD /openmp /c f1.c f2.c` `icl /MD /Qopenmp /c f3.c f4.c` `link f1.obj f2.obj f3.obj f4.obj /out:app.exe /nodefaultlib:vcomp libiomp5md.lib`

The following example shows the use of interprocedural optimization by the Intel C++ Compiler on several files, the Visual C++ Compiler compiles several files, and the Visual C++ linker links the object files to create the executable:

Type of File | Commands
--- | ---
C source, dynamic link | `icl /MD /Qopenmp /O3 /Qipo /Qipo-c f1.c f2.c f3.c` `cl /MD /openmp /O2 /c f4.c f5.c` `cl /MD /openmp /O2 ipo_out.obj f4.obj f5.obj /Feapp /link /nodefaultlib:vcomp libiomp5md.lib`

The first command uses the Intel C++ Compiler to produce an optimized multi-file object file named ipo_out.obj by default (the /Fe option is not required). The second command uses the Visual C++ Compiler to produce two more object files. The third command uses the Visual C++ cl command to link all three object files using the Intel C++ Compiler OpenMP library.

## Using Intel OpenMP Libraries from Visual Studio

When using systems running Windows, you can make certain changes in the Visual C++ Visual Studio* 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:

1. Open the project's property pages in from the main menu: Project > Properties (or right click the Project name and select Properties) .

2. Select Configuration Properties > Linker > General > Additional Library Directories.

3. Enter the path to the Intel®-provided compiler libraries. For example, for an IA-32 architecture system (C++ only), 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:

1. Open the project's property pages in from the main menu: Project > Properties (or right click the Project name and select Properties).

2. Select Configuration Properties > Debugging > Environment.

3. Enter the path to the Intel®-provided compiler libraries. For example, for an IA-32 architecture system (C++ only), 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:

1. Open the project's property pages in from the main menu: Project > Properties (or right click the Project name and select Properties).

2. Select Configuration Properties > Linker > Command Line > Additional Options.

3. Enter the OpenMP library name and the Visual C++ linker option, /nodefaultlib.

## Command-Line Examples, Linux

To compile and link (build) the entire application with one command using the Intel OpenMP libraries, specify the following Intel C++ Compiler command on Linux platforms:

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

By default, the Intel C++ Compiler performs a dynamic link of the OpenMP libraries. To perform a static link (not recommended), add the option -qopenmp-link=static. The option -qopenmp-link controls whether the linker uses static or dynamic OpenMP libraries on Linux and macOS* systems (default is -qopenmp-link=dynamic).

You can also use the icc/icpc compilers with the gcc/g++ compilers to compile parts of the application and create object files (object-level interoperability).

In this example, gcc compiles the C file foo.c (the gcc option -fopenmp enables OpenMP support), and the Intel C++ Compiler links the application using the Intel OpenMP library:

Type of File | Commands
--- | ---
C source | `gcc -fopenmp -c foo.c`
C++ source | `g++ -fopenmp -c foo.cpp`

When using gcc or the g++ compiler to link the application with the Intel C++ 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`

You can mix object files, but it is easier to use the Intel C++ 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 -qopenmp -c bar.c` (Linux and macOS*) `icc -qopenmp foo.o bar.o` (Linux and macOS*)

You can mix OpenMP object files compiled with GCC, Intel C++ Compiler, or .

### 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 to link all the objects:

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

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

Alternatively, you could use the Intel C++ 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 -qopenmp -c ibar.c` `icc -qopenmp foo.o bar.o -lgfortranbegin -lgfortran`

## Command-Line Examples, macOS*

To compile and link (build) the entire application with one command using the Intel OpenMP libraries, specify the following Intel C++ Compiler command on macOS* platforms:

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

By default, the Intel C++ Compiler performs a dynamic link of the OpenMP libraries. To perform a static link (not recommended), add the option -qopenmp-link=static. The option -qopenmp-link controls whether the linker uses static or dynamic OpenMP libraries on Linux and macOS* systems (default is -qopenmp-link=dynamic).

You can also use the Intel C++ Compiler icc/icpc/icl with gcc/g++ compilers to compile parts of the application and create object files (object-level interoperability).

### Note

Mixed compiling using Intel C++ Compiler with GCC Compilers is possible only on older macOS* platforms. The latest macOS* v10.x platforms do not include the GCC Compiler, and the Clang Compiler included in the latest macOS* 10.x does not support OpenMP implementation. Future versions of Clang Compiler may support OpenMP implementation.

In this example, icl or icc compiles the C file foo.c,icpc compiles the file ifoo.cpp, the option Qopenmp (Windows) or qopenmp (Linux or macOS*) enables OpenMP support, and the Intel C++ Compiler links the application using the Intel OpenMP library:

Type of File | Commands
--- | ---
C source | `icc -qopenmp -c foo.c`
C++ source | `icpc -qopenmp -c ifoo.cpp`

### Note

GCC is absent on macOS* v10.9 and later. However, you may install GCC along with the Intel C++ Compiler.

You can mix object files, but it is easier to use the Intel C++ 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 | `icx -qopenmp -c bar.c` `icx -qopenmp foo.o bar.o`

Alternatively, you could use the Intel C++ 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 | `icc -qopenmp -c ibar.c` `icc -qopenmp foo.o bar.o -lgfortranbegin -lgfortran`

Parent topic: OpenMP* Library Support

## See Also

openmp, Qopenmp compiler option
Using IPO
OpenMP* Support Libraries
qopenmp-link, Qopenmp-link compiler option