#ifdef / #ifndef和#endif

Question

I have a piece of code that has to be run both on a CPU and CUDA-GPU and an other piece of code running on CPU alone. #define ENABLE_CUDA is what i 'turn on' to enable the CUDA code in the entire application. Here is what my code looks like....

# define ENABEL_CUDA is the preprocessor directive to turn ON/OFF CUDA code.

CPU and GPU code --This piece of code has to be executed irrespective of whether CUDA is ON / OFF.

standalone CPU code alone -- This piece of code has to be executed only if CUDA is OFF.

My solution is :

#ifdef ENABLE_CUDA

  CPU AND GPU code
# else
  CPU AND GPU code
  standalone CPU code 
# endif

But this involves code duplication (CPU AND GPU code) in both the ifdef and else blocks, I would like to avoid it.

How can I accomplish it? What has to be done inorder to avoid duplication of code ? Any pointers regarding this appreciated...

Answer 1

#ifdef ENABLE_CUDA

  CPU AND GPU code
# else
  CPU AND GPU code
  standalone CPU code 
# endif

Is equivalent to:

  CPU AND GPU code
# ifndef ENABLE_CUDA
  standalone CPU code 
# endif

In general, if code is common to both if and else you can move it out of both.

Answer 2

Why not simply use:

CPU AND GPU code

#ifndef ENABLE_CUDA
  standalone CPU code 
# endif

Answer 3

Beside what the others have already said,

#ifndef ENABLE_CUDA
# define __device__
#endif

will take you a long way writing functions that run on the device if CUDA is present or on the host if not, without code duplication.