Silence of unused variable warning

It would be nice to silence the warnings caused by unused variables. There are several ways to do it:

do not name the unused argument (not preferable),
use [[maybe_unused]] (since C++17) in function definition,
typecast the unused variable (void) var. This approach is used in Qt. For example consider the following function:

   static std::string name( CudaStatusType error_code )
   {
#ifdef HAVE_CUDA
      return cudaGetErrorName( error_code );
#else
    (void) error_code;
      throw CudaSupportMissing();
#endif
   }

The approach in Qt discussed here is the following:

#define UNUSED(var) (void) var

Then, the warning can be silenced by UNUSED(error_code);.