# 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 targets in the subdirectory will not be included in the `ALL` target of the parent directory by default, and will be excluded from IDE project files. Users must explicitly build targets in the subdirectory. This is meant for use when the subdirectory contains a separate part of the project that is useful but not necessary, such as a set of examples. Typically the subdirectory should contain its own `project()` command invocation so that a full build system will be generated in the subdirectory (such as a Visual Studio IDE solution file). Note that inter-target dependencies supersede this exclusion. If a target built by the parent project depends on a target in the subdirectory, the dependee target will be included in the parent project build system to satisfy the dependency.

Added 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.