It's not either "build-system dependent mess" or "everything in header." The alternative to "everything in header" is "header file has interface, .c file has implementation." Then you add the .c file to your project, include the .h file, and it works better than "everything in .h" since instead of 20,000 lines all other .c files in user projects have to see only a few hundred lines, which compiles faster. And that's how C projects were supposed to be organized since the beginnings. You don't have to have dynamically bound files if that isn't needed. Some licenses insist on dynamical linking, but when you make your library, your decisions on how it's linked are independent of your decision to stuff the implementation in .h.