I just want to point out, that unless you're running a professionally managed software project with developers and testers and test devices for all branches of that #ifdef tree (hopefully just two, but...), code inside #ifdefs is a big problem. If you need to change it, you often have to change all branches. But if you can't conveniently test it, can't possibly even check if it compiles without installing a new full cross-platform SDK, how confidently can you make the change? Or do you just add #error on the #ifdef branch you didn't touch, so the next person compiling for the other branch is force to fix that branch too?

For open source application development, that kind of #ifdefs are bad bad bad. They all should be hidden inside framework code, so the application developer community doesn't need to care. Isn't that the whole point of the framework?

Seriously, no to requiring #ifdefs for cross-platform operation! I mean, with enough #ifdefs, every code can be cross-platform...