Platform C Preprocessor Definitions

Question

Hey all, I'm writing a small library in C++ that I need to be able to build on quite a few different platforms, including iPhone, Windows, Linux, Mac and Symbian S60. I've written most of the code so that it is platform-agnostic but there are some portions that must be written on a per-platform basis.

Currently I accomplish this by including a different header depending on the current platform but I'm having trouble fleshing this out because I'm not sure what preprocessor definitions are defined for all platforms. For windows I can generally rely on seeing WIN32 or _WIN32. For Linux I can rely on seeing _UNIX_ but I am less certain about the other platforms or their 64-bit variants. Does anyone have a list of the different definitions found on platforms or will I have to resort to a config file or gcc parameter?

Cheers, CH

Answer 1

Neither the C nor the C++ standards define such symbols, so you are going to be at the mercy of specific C or C++ implementations. A list of commonly used symbols would be a useful thing to have, but unfortunately I haven't got one.

Answer 2

I don't think there exists a universal list of platform defines judging by the fact that every cross-platform library I have seen has an ad-hoc config.h full of these stuff. But you can consider looking at the ones used by fairly portable libraries like libpng, zlib etc.

Here's the one used by libpng

Answer 3

The definitions are going to be purely up to your compiler vendor. If you are using the same compiler (say, gcc) on all your platforms then you will have a little bit easier time of it.

You might also want to try to instead organize your project such that most of the .h files are not platform dependent. Split your implementation (cpp files) into separate files; one for the nonspecific stuff and one for each platform. The platform specific ones can include 'private' headers that only make sense for that platform. You may have to make adapter functions to get something like this to work 100% (when the system libs take slightly differed arguments) but I have found it to be really helpful in the end, and bringing on a new platform is a whole lot easier in the future.

Answer 4

I have this sourceforge pre-compiler page in my bookmarks.