Creating flow diagrams from sources?

I have been looking around the web for an app to convert C++ source code to flow diagrams. I'm looking in the wrong places or nothing exists other than a few commercial apps. I was hoping the Umbrello tool could help, but that does not convert anything directly. Is there a way to do this? I want to map the entire docbook process. As I am still very much a novice C++ coder, I am in over my head trying to trace how everything connects. The process should be documented for the wiki. Ideas? Thanks. Darrell