Build a library

In addition to compiling executable applications, CMake also supports generating library artifacts. Use the add_library() function to define a STATIC library (.a or .lib) or a SHARED library (.so or .dll). This is similar to add_executable().

cmake_minimum_required(VERSION 3.28)
project(my-project)
add_library(my-lib STATIC my-lib.c)
add_library(my-lib SHARED my-lib.c)

int add(int a, int b) {
    return a + b;
}

cmake -B build
cmake --build build
file build/my-lib.a
file build/my-lib.so

Note that the add_library() declaration makes use of CMake syntax that doesn't look like what you might be used to in other languages like C, C++, or Python. The STATIC and SHARED enum-like words fit into the <type> slot in the function definition.

add_library(<name> [<type>] [EXCLUDE_FROM_ALL] <sources>...)

Add a library target called <name> to be built from the source files listed in the command invocation.

The optional <type> specifies the type of library to be created:

• STATIC: An archive of object files for use when linking other targets.
• SHARED: A dynamic library that may be linked by other targets and loaded at runtime.

If no <type> is given the default is STATIC or SHARED based on the value of the BUILD_SHARED_LIBS variable.

— add_library | CMake Documentation

You can compile libraries using the same cmake -B build and cmake --build build incantation as was used in the executable example. The output formats and how the compilation process happens is all defined by the CMakeLists.txt file and not command arguments.