How to use TARGET_OS_WIN32 properly?

Question

In my program, I've got a console clear screen command that's of course different between PC and Mac. So I've got this:
#if TARGETOSWIN32
system("cls");
#else
system("clear");
#endif
But the PC doesn't seem to recognize the macro - it just skips to the #else part. Is TARGETOSWIN32 predefined in a library somewhere, or do I need to define it? If it's predefined, what library do I need to include (or is there something else I need to do)? If I need to define it, how do I do that?
Thanks.

Answer 1

Ah, ok, so I could have used MSCVER instead, and that would have worked as well, as long as I compiled in VS? However, it wouldn't work for me, because I'm not compiling in VS - I'm compiling in an opensource IDE called DevC++ (I only have the educational version of VS which won't create an exe).
When I compile on DevC++, the build works as it should on Windows (calling "cls" instead of "clear").
Also, isn't Xcode based on GCC? I used Xcode to compile the code on the Mac, and it works fine (thus I'm assuming _WIN32 is not defined, because it's calling "clear", as it should on the Mac).