> because i dont know in which platform the final application will be run
And neither do the applications you've looked at.

You don't just "run" a C program on a machine, you have to compile it first (or 'make' in larger programs). This act of creating a runnable program is where the choice of actual implementation takes place.

> i have to consider quite a lot of platoforms before i am assured that my application will run smoothly..
That's the way it is. Grab any portable library (say http://www.zlib.net/) and you'll see all sorts of portability hackery.