Visualizing a huge C++ project using Doxygen + Graphviz

Question

I've inherited a large C++ project which I need to port to Linux. There are over 200,000 lines of source in this project spread across more than 300 files. It would be tremendously helpful to have a visual dependency/include tree to refer to for this project so that I can get a general feel for the application's internal structure. This would also help me to locate the "fault lines" between the core modules and Windows header files so that I can stub them out later.

The class viewer in Visual Studio simply isn't cutting it. I was reading around, and learned that Doxygen is a commonly used tool for listing dependencies. I'm much more of a visual person, and found that this wasn't so helpful. Fortunately, I learned about the Graphviz plugin, using something called "Dot" that has enabled me to generate dependency trees for parts. Unfortunately, hundreds of smaller dependency trees are generated for specific files, rather than having one large one as I'd hoped for. Here are a couple of examples:

As you can see (I hope), Doxygen/GraphViz seem to give up when the graph gets too large and gray out the child nodes. I then have to go to the graph for that specific node if I want to see what's further down the tree. Not only does this limit the visual helpfulness of the graph, but if the child node depends on any of the nodes from the original graph, these nodes will be shown again. This is leading to lots of duplicate connections that make it very hard to conceptually isolate the graph from any given file. As a result, I feel like I'm "zoomed in" and still can't see the whole picture.

I've tried playing around with the DOT_GRAPH_MAX_NODES setting in the Expert view in Doxygen, but this doesn't seem to affect the scope of the graphs that are being generated. From the output generated from any given run, it seems like Doxygen itself is generating hundreds of graph files, and Graphviz is just faithfully generating graphs for each one. Is there any known way to make Doxygen generate one large graph file instead of hundreds of smaller ones?

Alternatively, are there any free visual graphing solutions out there which know how to handle complicated C++ project files with nested pre-processor directives, MIDL interfaces, and manually defined include paths the way Doxygen does?

My searches are finding general graphing utilities (or questions about them), but nothing specific to large C++ projects. Surely with all the coding that's been done over the years somebody must have such a tool!

Thanks, -Alex

Answer 1

You can use the XML files generated by doxygen, and merge them into a single giant dot-format graph file (using xml stylesheet or similar), then run graphviz on it.

Doxygen automatically invoking graphviz is most useful when the number of graphs is high. For a single graph, automatically creating the content is important, but automatically calling dot, not so much.