如何在Visual C ++中有条件地包含不存在的文件？

Question

I'm using Visual C++ to build and test a project, but I'll also be using it on other platforms. I started the code initially on a different platform.

In some of my class headers I need to include a file which is specific to the other platform, however, this file doesn't exist in the Visual C++ workspace.

I've tried using code like this:

 #if TARGET == OTHERPLATFORM
 #include "themissingfile.h"
 #endif

where TARGET is defined elsewhere as WINDOWS

 #define TARGET WINDOWS

However, I still get a compiler error stating that "themissingfile.h" cannot be found. It appears like the precompiler is processing the include before the if. What's the best way to get around this? I suppose I could just create a blank "themissingfile.h" in the Visual C++ source folder, but it seems to me like there should be a better solution.

Answer 1

Use _WIN32 macro instead:

#ifndef _WIN32
#include "themissingfile.h"
#endif

_WIN32 is defined for both 32-bit and 64-bit builds. See C/C++ Predefined Macros .

Answer 2

#define TARGET WINDOWS does not set TARGET to the string WINDOWS: it sets it to whatever WINDOWS is defined to. Most likely this happens:

  #define WINDOWS          // Sets WINDOWS to 0
  #define OTHERPLATFORM    // Sets OTHERPLATFORM to 0
  #define TARGET WINDOWS   // Sets TARGET to 0

  #if TARGET == OTHERPLATFORM // Evaluates to 0==0, so true