Sirf version to be available at C++ level

[paskino]

With #872 version strings have been added at Python and MATLAB level, however this should be available in C++.

[paskino]

I suggest this to be made available from the output of git describe as we do in CIL.

[KrisThielemans]

I'm not a fan of git describe. For instance, on STIR master this gives me

$ git describe
rel_4.1.0-705-g256e56bdc

That implies we are at version 4.1, but actually STIR master is well on the way for 5.0. In particular, it is no longer backwards compatible with 4.1. Hence our CMakeLists.txt sets the version to 5.0.0-prealpha. While git describe allows nice not to have to update versions in CMake files, I think it is impossible to do this automatically such that the logic is preserved.

PS: CIL really shouldn't use git but find_package(git), and use GIT_EXECUTABLE.

[paskino]

git describe finds the most recent tag that is reachable from a commit. If the tag points to the commit, then only the tag is shown. Otherwise, it suffixes the tag name with the number of additional commits on top of the tagged object and the abbreviated object name of the most recent commit.

rel_4.1.0-705-g256e56bdc means you are 705 commits from rel_4.1.0 which IMHO means a lot has changed.

I find it rather clean, nice, and mainly it gives a single origin to the version, i.e. the tag in the repository.

[KrisThielemans]

it is informative, but it doesn't allow us to do

#if STIR_VERSION  500000
  bla
#else
  bloe
#endif

Having the complete git info as well could be useful of course. What I would then certainly want to avoid is whenever a commit happens, everything gets rebuilt because version.h changes. I'd recommend doing that via a git_version.h, which is only included in git_version.cxx, which would then be rebuilt, but that's presumably quick enough (if it doesn't depend on anything else).