noop - What's a portable way to implement no-op statement in C++?

Question

One in a while there's a need for a no-op statement in C++. For example when implementing assert() which is disabled in non-debug configuration (also see this question):

#ifdef _DEBUG
#define assert(x) if( !x ) { 
                     ThrowExcepion(__FILE__, __LINE__);
                  } else {
                     //noop here 
                  }
#else
#define assert(x) //noop here
#endif

So far I'm under impression that the right way is to use (void)0; for a no-op:

(void)0;

however I suspect that it might trigger warnings on some compilers - something like C4555: expression has no effect; expected expression with side-effect Visual C++ warning that is not emitted for this particular case but is emitted when there's no cast to void.

Is it universally portable? Is there a better way?

Answer 1

The simplest no-op is just having no code at all:

#define noop

Then user code will have:

if (condition) noop; else do_something();

The alternative that you mention is also a no-op: (void)0;, but if you are going to use that inside a macro, you should leave the ; aside for the caller to add:

#define noop (void)0
if (condition) noop; else do_something();

(If ; was part of the macro, then there would be an extra ; there)