Using UNREFERENCED_PARAMETER macro

Question

I'm using \W4 warning level on Visual Studio and I'm writing a Windows program.

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)

All these parameters are not used in my application, so I get warnings at compile time.

I know there are two ways of dealing with this:

1. Commenting parameters HINSTANCE /*hInstance*/ ...

2. Using the UNREFERENCED_PARAMETER macro

   int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
   {
     UNREFERENCED_PARAMETER(hInstance);
     UNREFERENCED_PARAMETER(hPrevInstance);
     UNREFERENCED_PARAMETER(lpCmdLine);
     UNREFERENCED_PARAMETER(nCmdShow);
   

Which one is the correct one? Which one is the safer to use? Are there any problems with using the macro?

Answer 1

I would prefer commenting the parameters.

The macro UNREFERENCED_PARAMETER is defined in winnt.h and therefore not portable.

And if later you do reference it, you might overlook to remove the macro.

Edit: With C++17 you can now use the [[maybe_unused]] attribute. This is useful for code depending on preprocessor macros:

void foo( [[maybe_unused]] int value )
{
#ifdef USE_VALUE
   useValue(value);
#endif
}

Now there won't be warnings even if USE_VALUE is undefined.