cmake-git-hash module

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.

Setup

To use GitHash in your project, you need to:

• Clone the project in some sub-folder of your project, and add to your main CMakeLists.txt file the following line:

  add_subdirectory(<GitHash_Dir_Path>)`
  

• Add the following include where you need it:

  #include "GitHash.hpp"
  

• Use these variables in your C++ files:

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

• In CMake, link your project to the GitHash library using the ${GITHASH_LIBRARIES} variable:

  target_link_libraries(your_project "${GITHASH_LIBRARIES}")
  

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.

Customization

Output Files Names and Path

If for any reason you might want to have the output files have different names and/or reside in a different folder than the default ones, you can configure them via the following CMake variables: GitHash_OutputDir, GitHash_CppFilename and GitHash_CacheFilename. For example, you might want to run:

cmake -DGitHash_OutputDir=MyCustomFolder

Additional Fields

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

Other non-Git Commands

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.

Credits

This library was developed with the help of this blog post and based on this repo.