# Creating 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.

To build a static library on Linux*:

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

       [invocation] -c my_source1.cpp my_source2.cpp my_source3.cpp

   Where the [`invocation`] is `icpc`.

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:

       [invocation] main.cpp my_lib.a

   Where the [`invocation`] is `icpc`.

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

    [invocation] -L/cpp/libs main.cpp my_lib.a

Where the [`invocation`] is `icpc`.

To build a static library on macOS*:

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

       [invocation] -fpic -o mylib.a -staticlib my_source1.cpp my_source2.cpp my_source3.cpp

   Where the [`invocation`] is `icpc`.

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

       [invocation] main.cpp my_lib.a

   Where the [`invocation`] is `icpc`.

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

    [invocation] -L/cpp/libs main.cpp my_lib.a

Where the [`invocation`] is `icpc`.

If you are using Interprocedural Optimization, see the topic on Creating a Library from IPO Objects 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.

To build a shared library on Linux:

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

       [invocation] -fPIC -c my_source1.cpp my_source2.cpp my_source3.cpp

   Where the [`invocation`] is `icpc`.

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

       [invocation] -shared -o my_lib.so my_source1.o my_source2.o my_source3.o

   Where the [`invocation`] is `icpc`.

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

       [invocation] main.cpp my_lib.so

   Where the [`invocation`] is `icpc`.

To build a shared library on macOS*:

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

       [invocation] -fPIC -o my_lib.so -dynamiclib my_source1.cpp my_source2.cpp my_source3.cpp

   Where the [`invocation`] is `icpc`.

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

       [invocation] main.cpp my_lib.dylib

   Where the [`invocation`] is `icpc`.

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

Using Intel Shared Libraries
/LD compiler option
/MD compiler option
/MT compiler option