# add_subdirectory

Add a subdirectory to the build.

    add_subdirectory(source_dir [binary_dir] [EXCLUDE_FROM_ALL] [SYSTEM])

Adds a subdirectory to the build. The `source_dir` specifies the directory in which the source `CMakeLists.txt` and code files are located. If it is a relative path, it will be evaluated with respect to the current directory (the typical usage), but it may also be an absolute path. The `binary_dir` specifies the directory in which to place the output files. If it is a relative path, it will be evaluated with respect to the current output directory, but it may also be an absolute path. If `binary_dir` is not specified, the value of `source_dir`, before expanding any relative path, will be used (the typical usage). The `CMakeLists.txt` file in the specified source directory will be processed immediately by CMake before processing in the current input file continues beyond this command.

If the `EXCLUDE_FROM_ALL` argument is provided then the `EXCLUDE_FROM_ALL` property will be set on the added directory. This will exclude the directory from a default build. See the directory property `EXCLUDE_FROM_ALL` for full details.

New in version 3.25: If the `SYSTEM` argument is provided, the `SYSTEM` directory property of the subdirectory will be set to true. This property is used to initialize the `SYSTEM` property of each non-imported target created in that subdirectory.