I would like to detect whether the OS I'm compiling on is Windows. Is there a simple macro I can check to verify that?
[Edit: I assume you want to use compile-time macros to determine which environment you're on. Maybe you want to determine if you're running on Wine under Linux or something instead of Windows, but in general, your compiler targets a specific environment, and that is either Windows (DOS) or it isn't, but it's rarely (never?) both.]
Some compilers offer macros to indicate a Windows build environment. But these will vary from compiler to compiler, and even on the same compiler on Windows if the target environment is not exclusively windows. Usually it's
__WIN32__, but not always.
#if defined (__WIN32__) // Windows stuff #endif
Sometimes it can be
__CYGWIN32__, or possibly just the compiler indicator (
If you know the environment you'll be building in (from the makefile) then you can usually pass in the
#define on the command line, like "
g++ -D __WIN32__ yourfile.c".
There are a number of different ways to detect compilation, host, and runtime environments. All depending on exactly what you want to know. There are three broad types of environments:
If you are cross-compiling, the build and host environment can be completely different (this is common when building embedded applications, but not very common when building desktop/server apps), and you typically cannot run the compiled binary on the system used to compile it. Otherwise, the host environment must be compatible with the build environment: for example, building an application on XP which will run on Vista.
C preprocessor macros can not be used to tell you the details of the host system (i.e. what you are running on); they can only tell you what the code was compiled for. In the windows case, the two most important macros are:
_MSC_VERtells you that you the the program is being compiled with Microsoft Visual C/C++. Well, almost.
_MSC_VERis also defined when using Intel's C++ compiler which is intended to be a drop-in replacement for Visual C++.
There are a bunch of other macros described in the Visual Studio documentation.
If you want to know which exact version of Windows you are using, you'll have to use runtime functions such as GetVersion() (as described in other answers).
You might get more specific answers if you told us exactly what you want to check for.