All, I've just released the preliminary version of a C API for accessing deltacloud, called dcloudapi. You can get it here:
git clone git://git.fedorahosted.org/git/deltacloud/dcloudapi.git/
Note that it is still early on in the development, so the API is subject to change, but right now it implements all of the methods that the ruby client does. I'm already using it to build the condor GAHP, so it is somewhat useful, but if you have questions or comments about it, please let me know. Any discussion about it should be sent to deltacloud-devel for now.
deltacloud-devel@lists.fedorahosted.org