Is it possible to create a null function that will not produce warnings?

I have a logger in a c++ application that uses defines as follows:

#define FINEST(...) Logger::Log(FINEST, _FILE, __LINE, __func, __VA_ARGS_)

However what I would like to do is to be able to switch off these logs since they have a serious performance impact on my system. And, it's not sufficient to simply have my Logger not write to the system log. I really need to get rid of the code produced by the logs.

In order to do this, I changed the define to:

#define FINEST(...)

Which works, but this produces a whole bunch of warning in my code since variables are unused now. So what I would like to have is a sort of NULL FUNCTION that would not actually exist, but would not produce warnings for the unused variables.

So, said another way, I would like it to compile with no warnin开发者_JS百科gs (i.e. the compiler thinks that the variables are used for a function) but the function does not actually exist in the application (i.e. produces no performance hit).

Is this possible?

Thanks!

Have you considered turning off that particular warning of your compiler?
It's probably not a good idea, but if you need a quick and dirty solution...

You could define an empty function with unnamed parameters:

void nullFunc(int, int, int, const char*, ...) {
}

Then redefine your macro to call this function:

#define FINEST(...) nullFunc(FINEST, _FILE, __LINE, __func, __VA_ARGS_)

template<bool implemented>
void Logger::Log( ... );

template<>
void Logger::Log<true>( ... )
{
  // with implementation
}

template<>
void Logger::Log<false>( ... )
{
  // without implementation
}

// USE:
#define FINEST(...) Logger::Log<true>(FINEST, _FILE, __LINE, __func, __VA_ARGS_)
// or
#define FINEST(...) Logger::Log<false>(FINEST, _FILE, __LINE, __func, __VA_ARGS_)

// EVEN BETTER (w/o macro):
// flag to switch on/off logging
const bool with_log = true; // or =false

// use   
Logger::Log<with_log>( /* place arguments here */ );

On comeau and GCC, the warning disappears if you wrap the variables into a sizeof:

#define FINEST(...) ((void)sizeof(__VA_ARGS__))

To avoid warnings on GCC about that the left or right side of the comma operator has no effect (if it expands to sizeof(a, b) for example), you can introduce a debug-nullify type that has its own comma operator:

struct debug_nullify { };

// doesn't need a definition
template<typename T>
debug_nullify operator,(debug_nullify, T const &);

#define FINEST(...) ((void)sizeof(debug_nullify(), __VA_ARGS__))

The benefit of sizeof is that argument expressions are not evaluated.

I would reccomend removing the declarations in release too:

int somefunc(int foo, int bar, void* baz)
    {
    DEBUGVAR(Logger,log);
    int othervar;
    /* stuff */
    MAYBELOG(log,"something happened: %i",othervar);
    /* other stuff */
    return 0;
    }

in define:

#if DEBUGLEVEL>0
#define DEBUGVAR(type,...) type __VA_ARGS__
#define MAYBELOG(logger,str,...) logstuff(logger,__FLIE__,__LINE__,str,__VA_ARG__)
#else
#define DEBUGVAR(type,...)
#define MAYBELOG(logger,str,...)
#endif