Detecting if OS is Windows???

This may sound stupid but I do want to ask it to be sure.
If you have a cross platform application which can run under a Windows OS and Mac OS, in example,
is there a way to detect if that OS is a Windows OS and if it actually is a Windows OS, are you then able to use Windows code?

Hi, this post may answer your question.

http://predef.sourceforge.net/index.php
You probably want some #if type stuff around the OS specific parts of your code.

If you do it carefully, you should have
win.cpp - all the windows specific code
mac.cpp - all the mac specific code
Both these files provide the same interface to
main.cpp - all the independent code