API for reading the gnucash file

[hendrik at topoi.pooq.com]

I have a C++ propgram that reads a gnucash file and extracts relevant 
information.

I find that I have to revise it regularaly when the file format changes 
during gnucash upgrades.  Now this is not a huge chore, but I've heard 
that there is an API I could be using to do this so that
  (a) I don't have to keep updating my code
  (b) it will still run properly, even if gnucash starts to use a real 
data base.

Where do I find this API and its documentation?

-- hendrik