Cross platform C++ code architecture

Question

I'm having a bit of a go at developing a platform abstraction library for an application I'm writing, and struggling to come up with a neat way of separating my platform independent code from the platform specific code.

As I see it there are two basic approaches possible: platform independent classes with platform specific delegates, or platform independent classes with platform specific derived classes. Are there any inherent advantages/disadvantages to either approach? And in either case, what's the best mechanism to set up the delegation/inheritance relationship such that the process is transparent to a user of the platform independent classes?

I'd be grateful for any suggestions as to a neat architecture to employ, or even just some examples of what people have done in the past and the pros/cons of the given approach.

EDIT: in response to those suggesting Qt and similar, yes I'm purposely looking to "reinvent the wheel" as I'm not just concerned with developing the app, I'm also interested in the intellectual challenge of rolling my own platform abstraction library. Thanks for the suggestion though!

Answer 1

I'm using platform neutral header files, keeping any platform specific code in the source files (using the PIMPL idiom where neccessary). Each platform neutral header has one platform specific source file per platform, with extensions such as *.win32.cpp, *.posix.cpp. The platform specific ones are only compiled on the relevent platforms.

I also use boost libraries (filesystem, threads) to reduce the amount of platform specific code I have to maintain.

It's platform independent classes declarations with platform specific definitions.

Pros: Works fairly well, doesn't rely on the preprocessor - no #ifdef MyPlatform, keeps platform specific code readily identifiable, allows compiler specific features to be used in platform specific source files, doesn't pollute the global namespace by #including platform headers.

Cons: It's difficult to use inheritance with pimpled classes, sometimes the PIMPL structs need their own headers so they can be referenced from other platform specific source files.