This is a C++ class, together with non-object-oriented C and Fortran 90 bindings, that implement access to an FCIDUMP file as produced by the Full CI code (Computer Physics Communications Volume 54, Issue 1, April 1989, Pages 75–83, doi:10.1016/0010-4655(89)90033-7; http://bitbucket.org/pjknowles/fci), as well as Molpro via its fci,dump facility.
Pages describing the API can be found at https://molpro.github.io/fcidump