ctags is very useful. There are two steps involved. First run the program ctags on all your source and include directories. This creates a file named 'tags' in the local directory. ctags *.c *.h would do fine if all your source is in a single directory. When you work with source in multiple directories, it can be worth running ctags in multiple locations. Then, within vi, with your cursor on any function, defined type or variable use ctl-] to go to the definition of that entity. Use etags if you're using emacs.
