Managing CMake Build Artifacts: Cleaning Your Project
CMake is a powerful cross-platform build system generator. However, as projects grow, the build directory can accumulate numerous generated files (like CMakeFiles, CMakeCache.txt, and object files). This can lead to confusion, increased disk usage, and potential issues with incremental builds. This tutorial will explain how to effectively clean these artifacts to maintain a healthy and efficient development workflow.
Understanding CMake’s Build Process and Artifacts
CMake doesn’t directly "compile" your code. Instead, it generates build files (Makefiles, Visual Studio projects, Ninja build files, etc.) that are then used by a native build tool. This means CMake creates intermediate files and directories during its configuration step and during the build itself. Common artifacts include:
CMakeCache.txt: Stores cached variables and configurations used during CMake’s configuration step. This file can become outdated or contain incorrect values.CMakeFiles/: A directory containing CMake-generated source files used in the build process.- Generated build system files: (e.g.,
Makefile,.sln,build.ninja) These are created by CMake and used to drive the build process. - Object files (
.o,.obj): Compiled object files created during the build process. - Executables and Libraries: The final output of your build.
Cleaning CMake Build Artifacts
There are several ways to clean these artifacts, depending on your CMake version and build setup.
1. CMake’s Built-in clean Target (CMake 3.x and later)
CMake 3.x introduced a dedicated clean target. This is the recommended approach. To use it, you execute the following command in your terminal:
cmake --build <build_directory> --target clean
Replace <build_directory> with the path to your CMake build directory (e.g., build/). This command instructs CMake to execute the clean target defined in the generated build system, removing most build artifacts.
2. Removing the Entire Build Directory
A straightforward and often effective method is to simply delete the entire build directory. This ensures a completely clean slate.
rm -rf <build_directory>
Important: Be absolutely certain you are deleting the correct directory, as rm -rf is a powerful and irreversible command.
3. Manual Removal (Less Recommended)
While possible, manually deleting files and directories is error-prone and not recommended. You would need to identify all generated files and directories and delete them individually.
4. Utilizing make clean (If Using a Makefile Generator)
If you are using CMake to generate Makefiles, you can use the standard make clean command within your build directory.
cd <build_directory>
make clean
This will remove object files and other intermediate build products generated by the compiler. It won’t remove the CMake-generated files themselves (like CMakeCache.txt and the CMakeFiles directory).
Best Practices
- Out-of-Source Builds: Always perform builds in a dedicated build directory separate from your source code directory. This keeps your source code clean and makes it easier to clean the build artifacts without affecting your source files. This is highly recommended and avoids the need for a "distclean" equivalent.
- Version Control: Store your source code in a version control system (like Git). This provides a backup and allows you to easily revert to a previous state if needed.
- Regular Cleaning: Periodically clean your build directory to prevent it from becoming cluttered and to ensure that you are building with the latest configurations.
- Avoid In-Source Builds: Building directly in your source directory mixes generated files with source code, making cleaning and maintenance difficult. If you accidentally perform an in-source build, it’s usually best to delete the entire source directory and re-clone it from version control.
Why Doesn’t CMake Have a "Distclean" Target?
CMake doesn’t provide a "distclean" target that removes everything (including CMake-generated files and the build system itself) because CMake can execute arbitrary commands as part of the CMakeLists.txt file. Therefore, CMake cannot reliably track all generated files. A "distclean" target would give a false sense of security. The best practice of using out-of-source builds eliminates the need for such a target.