To use git branch and commit hash information in a CMake project, add the following lines to CMakeLists.txt

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# Get the current working branch
execute_process(
  COMMAND git rev-parse --abbrev-ref HEAD
  WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
  OUTPUT_VARIABLE GIT_BRANCH
  OUTPUT_STRIP_TRAILING_WHITESPACE
)

# Get the latest abbreviated commit hash of the working branch
execute_process(
  COMMAND git log -1 --format=%h
  WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
  OUTPUT_VARIABLE GIT_COMMIT_HASH
  OUTPUT_STRIP_TRAILING_WHITESPACE
)

execute_process() runs a single command or a sequence of commands and optionally gathers the output into CMake variables. The COMMAND is executed in WORKING_DIRECTORY and the STDOUT is saved to OUTPUT_VARIABLE after stripping trailing whitespace. The output of git log can be customized.

Now that these values are available for CMake, there are two ways to use them in a project.

• The easiest and simplest way is to use add_definitions() in CMakeLists.txt to make the variables available to the C/C++ project.

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add_definitions("-DGIT_COMMIT_HASH=${GIT_COMMIT_HASH}")
add_definitions("-DGIT_BRANCH=${GIT_BRANCH}")

• CMake also has the capability to generate a header file (or any file for that matter) with the configure_file() command. We can utilize this to generate a header file with these definitions and include it in the project.

You’ll need to include a template header file in the project source with some CMake specific annotations to achieve this. I choose to put version.h.in in the include folder in my source directory.

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#ifndef VERSION_H
#define VERSION_H

#define GIT_BRANCH "@GIT_BRANCH@"
#define GIT_COMMIT_HASH "@GIT_COMMIT_HASH@"

#endif

@GIT_BRANCH@ & @GIT_COMMIT_HASH@ will be substituted with the corresponding values obtained as the output of execute_process() command. The double quotes around the substitution variables are necessary if these variables have to be used as strings in a C/C++ project.

Add the following command to CMakeLists.txt to perform the generation.

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configure_file(
  ${CMAKE_SOURCE_DIR}/include/version.h.in
  ${CMAKE_BINARY_DIR}/generated/version.h
)

This will write a version.h file to generated directory of ${CMAKE_BINARY_DIR}. Next, the folder generated has to be added to the C/C++ INCLUDE_PATH in CMakeLists.txt

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include_directories(${CMAKE_BINARY_DIR}/generated)

Include version.h in a C/C++ file and you are done.

I’ve created a sample C project which uses this on Github.

PS: Ryan Pavlik has a CMake module for this available on Github. stackoverflow has a thread detailing it’s usage.