How can I check #ifdef in a DLL project, when the #define is in the executable project using the dll?

Question

I have a C++ Visual Studio 2015 project consisting of 1 Windows API executable, 1 windows console executable, and 1 dll shared by both executables.

I have a #define USEWINDOWS in the Windows API main.cpp file

I don't have this defined in the console app

In the DLL, I would like to do an #ifdef USEWINDOWS statement, but the scope of the #define seems to be only valid to the Win32 executable, not in the dll.

How can I extend this #define to the DLL without having it affect the undefined USEWINDOWS in the console app?

Thanks

Answer 1

The DLL is shared by both executables, hence there is only one implementation available and therefore you can't use implementation specific compilation flags.

You'll need a runtime flag, ie some API parameter which tells the DLL code that it is OK to use "windows stuff". Eg

api.h

void someAPI(...., bool useWindows);

dll.c

#include "api.h"

void someAPI(...., bool useWindows) {
  ...
  if (useWindows) {
     // do "windows stuff" here
  }
  ...
}

app.c

#include "api.h"
...
someAPI(...., true);

console.c

#include "api.h"
...
someAPI(...., false);

(not tested by compilation, but you should get the drift...)