If you want to get to know your code structure without taking an initial deep dive into the sources, you might be interested in tools that generate diagrams from code.
One such tool is CppDepend. It enables you to create various dependency diagrams between different parts of your sources. What's more, it allows you to query and filter the code based on various parameters. Whether you want to just grasp how the code is structured, discover what the dependencies are between different software components and how tightly they're coupled, or want to quickly locate parts with the most technical debt, you might be interested in this tool. It's proprietary, but offers a fully functional trial.
Some diagramming tools allow you to create code from class diagrams and class diagrams from code. Enterprise Architect enables you to take your class and interface diagrams and generate code in multiple languages. C++ is one of these, and allows UML class diagrams...