Difference between CMAKE_CURRENT_SOURCE_DIR and CMAKE_CURRENT_LIST_DIR

Question

The variables CMAKE_CURRENT_SOURCE_DIR and CMAKE_CURRENT_LIST_DIR may refer to different directories for a CMake list file that is included by another file with the include command. E.g., if a CMakeLists.txt is present in a directory project and contains the following directive

include(src/CMakeLists.txt)

then while src/CMakeLists.txt is being processed CMAKE_CURRENT_LIST_DIR will refer to project/src whereas CMAKE_CURRENT_SOURCE_DIR still points to the outer directory project.

CMAKE_CURRENT_LIST_DIR comes in handy when you need to locate resource files like template files or batch scripts that are located next to the CMakeLists.txt file currently being processed.

---

_{Note: When using the add_subdirectory() command rather than include(), the behavior is different, and when src/CMakeLists.txt is being processed, both variables will point to project/src.}

Definitions

CMAKE_SOURCE_DIR: Topmost folder(source directory) that contains a CMakeList.txt file. The value never changes in different scopes.

PROJECT_SOURCE_DIR: The nearest folder that contains CMakeList.txt file, with its own scope, that contains project() command.

CMAKE_CURRENT_SOURCE_DIR: The nearest folder that contains CMakeList.txt file with its own scope. (File do not need to contain project() command)

CMAKE_CURRENT_LIST_DIR: The folder that contains currently processed CMakeList.txt or .cmake file.

What I mean by its own scope is related to scoping rules. While include(file) command is not creating a new scope, add_subdirectory is creating a new scope which affects the PROJECT_SOURCE_DIR and CMAKE_CURRENT_SOURCE_DIR values.

Example

Let project structure be like below:

A/
=> CMakeList.txt
=> B/
   => CMakeList.txt

and let us assume we are printing all cmake variables by putting message command to CMakeList.txt file in subfolder B.

• If CMakeList.txt in folder A contains a line include("B/CMakeList.txt"), then

CMAKE_SOURCE_DIR will be source directory which is "path to project/A".

PROJECT_SOURCE_DIR will be "path to project/A", because include command does not create a new scope and the nearest CMakeList.txt file that has its own scope and contains project command is in folder A.

CMAKE_CURRENT_SOURCE_DIR will be "path to project/A", because include command does not create a new scope and the nearest CMakeList.txt file that has its own scope is in folder A.

CMAKE_CURRENT_LIST_DIR will be "path to project/A/B", because currently processed file is in subfolder B.

• If CMakeList.txt contains a line add_subdirectory("./B"), then

CMAKE_SOURCE_DIR will be source directory which is "path to project/A".

PROJECT_SOURCE_DIR will be "path to project/A/B", because add_subdirectory command creates a new scope and the nearest CMakeList.txt file that has its own scope and contains project command is in subfolder B.

CMAKE_CURRENT_SOURCE_DIR will be "path to project/A/B", because add_subdirectory command creates a new scope and the nearest CMakeList.txt file that has its own scope is in subfolder B.

CMAKE_CURRENT_LIST_DIR will be "path to project/A/B", because currently processed file is in subfolder B.

Reference: https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/Useful-Variables