CMake project, source and binary directory variables

Introduction

CMake variables like CMAKE_SOURCE_DIR are predefined variables in CMake that provide information about the build and source directory structure.

Directory Variables

1. CMAKE_SOURCE_DIR:

   • Represents the top-level directory containing the root CMakeLists.txt file.

2. CMAKE_BINARY_DIR:

   • Refers to the top-level build directory where CMake generates the build files.

3. PROJECT_SOURCE_DIR:

   • Refers to the source directory of the current project (set by project() in CMakeLists.txt).
   • If there are multiple nested projects, this variable changes for each.

4. PROJECT_BINARY_DIR:

   • Refers to the binary directory of the current project.
   • Similar to CMAKE_BINARY_DIR, but specific to the scope of the project.

5. CMAKE_CURRENT_SOURCE_DIR:

   • Represents the directory containing the CMakeLists.txt file currently being processed.
   • Different from CMAKE_SOURCE_DIR, as it reflects the current directory in a hierarchical project.

6. CMAKE_CURRENT_BINARY_DIR:

   • Points to the build directory corresponding to the CMAKE_CURRENT_SOURCE_DIR.

Summary

• CMAKE_* variables are global and refer to the top-level project.
• PROJECT_* and CMAKE_CURRENT_* variables adjust for subprojects and nested scopes.
• These variables help maintain a clean separation between source and build directories, which is a core principle of CMake.

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