Doxygen can build fully hyperlinked docs with complete source listing. It’ll give you an index of all the functions, structs and global variables, and makes it

Doxygen can build fully hyperlinked docs with complete source listing. It’ll give you an index of all the functions, structs and global variables, and makes it easy to drill down. If the project uses Cmake, you might look into Jet Brains’ Clion IDE, which has really great tools for code navigation, finding uses of a symbol, etc. As others have said, find the main function or other primary entry points and start reading. It can seem hopeless at first if the codebase is large, but persistence pays off. I often find making flow charts and graphing data relationships of key parts of the code to be really helpful.