Creating custom build targets in CMake

05 Oct 2023

CMake is a powerful build system generator that allows developers to configure and manage the build process of their projects. It provides a lot of flexibility and customization options to suit various project needs. In this article, we will explore how to create custom build targets in CMake, which can be useful for building specific files or directories with additional commands or scripts.

Introduction to CMake
CMake Build Targets
Creating Custom Build Targets
Example: Building Specific Files
Example: Building Directories
Conclusion

Introduction to CMake

CMake is an open-source, cross-platform build system generator that uses a single configuration file (CMakeLists.txt) to generate native build files for various build systems, such as Makefiles, Visual Studio solutions, or Xcode projects. It allows developers to write build scripts in a high-level language, making it easier to manage and automate the build process.

CMake Build Targets

In CMake, build targets are logical entities that represent the files or groups of files that need to be built. Examples of build targets include executable targets, library targets, or custom targets. CMake generates build rules based on these targets to build the desired output.

Build targets can depend on other build targets, which means that CMake will ensure that the dependencies are built first before building the target. This allows for a modular and efficient build process, where only the required parts are built.

Creating Custom Build Targets

To create a custom build target in CMake, we can make use of the add_custom_target command. This command allows us to specify a custom target name and the commands or scripts we want to execute when building that target.

Here is the syntax for add_custom_target:

add_custom_target(target_name [ALL | build_always]
                  [COMMAND command1 [ARGS...]]
                  [WORKING_DIRECTORY dir]
                  [DEPENDS depend1 [depend2 ...]]
                  [BYPRODUCTS files...]
                  [COMMENT comment]
                  [VERBATIM]
                  [USES_TERMINAL]
                  [COMMAND_EXPAND_LISTS]
                  [SOURCES src1 [src2 ...]])

target_name: The name of the custom target.
ALL | build_always: Specifies whether the target should be built always or only when explicitly requested.
COMMAND command1 [ARGS...]: The command or script to execute when building the target.
WORKING_DIRECTORY dir: The working directory for the command or script.
DEPENDS depend1 [depend2 ...]: The target dependencies.
BYPRODUCTS files...: The additional files generated by the target.
COMMENT comment: A comment to describe the target.
VERBATIM: Passes all arguments to the COMMAND unchanged.
USES_TERMINAL: Specifies whether the command should be run in a terminal.
COMMAND_EXPAND_LISTS: Expands list arguments for some commands.
SOURCES src1 [src2 ...]: The source files that should trigger a rebuild of the target.

Example: Building Specific Files

Let’s say you have a project with multiple source files, and you want to create a custom target to build only a specific set of files. You can achieve this by creating a custom target using the add_custom_target command and specifying the desired source files as dependencies.

add_custom_target(my_custom_target
    DEPENDS file1.cpp file2.cpp file3.cpp
)

In the above example, the my_custom_target depends on file1.cpp, file2.cpp, and file3.cpp. When you build the my_custom_target, only these files will be compiled and linked.

Example: Building Directories

In some cases, you may want to create a custom build target to build an entire directory or perform specific actions on the files in that directory. You can accomplish this by creating a custom target and defining the desired commands using the COMMAND option.

add_custom_target(my_custom_directory_target
    COMMAND echo "Building directory..."
    COMMAND make -C path/to/directory
    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
)

In the above example, the my_custom_directory_target executes the echo command and then runs make in the specified directory. The WORKING_DIRECTORY option sets the working directory for the commands.

Conclusion

Custom build targets allow us to extend and customize the build process in CMake. By creating custom targets, we can build specific files or directories with additional commands or scripts. This flexibility enables us to automate complex build tasks and create tailored build workflows for our projects.

Using the add_custom_target command, you can define the desired target name, specify commands or scripts to execute, set dependencies, and customize other options based on your project requirements.

By understanding how to create custom build targets in CMake, you can enhance your build system and better manage the compilation and linking process of your projects.

#programming #CMake

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