# Create Libraries

## Static Libraries

Libraries are simply an indexed collection of object files that are included as needed in a linked program. Combining object files into a library makes it easy to distribute your code without disclosing the source. It also reduces the number of command-line entries needed to compile your project.

Executables generated using static libraries are no different than executables generated from individual source or object files. Static libraries are not required at runtime, so you do not need to include them when you distribute your executable. At compile time, linking to a static library is generally faster than linking to individual source files.

These steps show how to build a static library on Linux using the `icpc` driver . See Invoke the Compiler for information about all available drivers.

1. Use the c option to generate object files from the source files:

       icpc -c my_source1.cpp my_source2.cpp my_source3.cpp

2. Use the GNU* tool ar to create the library file from the object files:

       ar rc my_lib.a my_source1.o my_source2.o my_source3.o

3. Compile and link your project with your new library:

       icpc main.cpp my_lib.a

If your library file and source files are in different directories, use the `Ldir` option to indicate where your library is located:

    icpc -L/cpp/libs main.cpp my_lib.a

To build a static library on macOS:

1. Use the following command to generate object files and create the library file:

       icpc -fpic -o mylib.a -staticlib my_source1.cpp my_source2.cpp my_source3.cpp

2. Compile and link your project with your new library:

       icpc main.cpp my_lib.a

If your library file and source files are in different directories, use the `Ldir` dir option to indicate where your library is located:

    icpc -L/cpp/libs main.cpp my_lib.a

If you are using Interprocedural Optimization, see the topic Create a Library from IPO Objects, which discusses using xiar.

## Shared Libraries

Shared libraries, also referred to as dynamic libraries or Dynamic Shared Objects (DSO), are linked differently than static libraries. At compile time, the linker insures that all the necessary symbols are either linked into the executable, or can be linked at runtime from the shared library. Executables compiled from shared libraries are smaller, but the shared libraries must be included with the executable to function correctly. When multiple programs use the same shared library, only one copy of the library is required in memory.

Linux

These steps show how to build a shared library on Linux using the `icpc` driver . See Invoke the Compiler for information about all available drivers.

1. Use options fPIC and c to generate object files from the source files:

       icpc -fPIC -c my_source1.cpp my_source2.cpp my_source3.cpp

2. Use the shared option to create the library file from the object files:

       icpc -shared -o my_lib.so my_source1.o my_source2.o my_source3.o

3. Compile and link your project with your new library:

       icpc main.cpp my_lib.so

macOS

These steps show how to build a shared library on macOS using the `icpc` driver

1. Use the following command to generate object files and create the library file:

       icpc -fPIC -o my_lib.so -dynamiclib my_source1.cpp my_source2.cpp my_source3.cpp

2. Compile and link your project with your new library:

       icpc main.cpp my_lib.dylib

Windows

Use the following options to create libraries on Windows:

Option | Description
--- | ---
/LD, /LDd | Produces a DLL. d indicates debug version.
/MD, /MDd | Compiles and links with the dynamic, multi-thread C run time library. d indicates debug version.
/MT, /MTd | Compiles and links with the static, multi-thread C run time library. d indicates debug version.
/Zl | Disables embedding default libraries in object files.

Parent topic: Libraries

## See Also

Use Intel Shared Libraries
Create a Library from IPO Objects
/LD compiler option
/MD compiler option
/MT compiler option