This module allows you to obtain the current branch, sha1, short sha1 and dirty flag directly within C++. It creates a static library called GitHash behind the scenes which contains these values as symbols you can use.

It additionally creates a cache of the last generated hash (and whether it was dirty) so it avoids recompilation as long as the current hash is equal to the last compiled one.

To use GitHash in your project, you only need to follow these steps:

• Copy the file GitHash.cmake in your project's cmake/Modules folder.
• Copy the file GitHash.hpp to your project's include directory.
• Add the following two lines to your main CMakeLists.txt file:

  include(${PROJECT_SOURCE_DIR}/cmake/Modules/GitHash.cmake)
  SetupGitHash()
  

• Use these variables in your C++ files:

  GitHash::branch;     // C-string
  GitHash::sha1;       // C-string
  GitHash::shortSha1;  // C-string
  GitHash::dirty;      // boolean
  

• In CMake, use target_link_libraries to link your project to the GitHash library (using the ${GITHASH_LIBRARIES} variable).

Note that currently the GitHash library is outputted in a subfolder of your PROJECT_BINARY_DIR. If this is not desired you will have to manually modify the script to specify your ideal output directory.

It is possible to add additional fields to read (for example, to read tags). For each new field, you need to:

• Modify the GitHash.hpp header file to expose the new field you want.
• Add the new field, and the appropriate git command to obtain its value, in the GitHash.cmake script. All modifications can be done briefly at the top of the CMake script:
  • Add a new CMake variable to variablesToRead
  • Add a new CMD_ variable containing the appropriate command to run
  • Add a new extern field (both declaration and definition) inside the string in the getCppContents function

The GitHash mechanism can be used more generally than git, since you could use arbitrary commands to generate and expose arbitrary values. If you do so, you may also want to change what is put in the cache so you can avoid recompilation when your commands return the same values. To do so, you just have to change the format of the cache file as returned by the genCache function.

This library was developed with the help of this blog post.