Variable arguments in a Macro - c

Question

I have a function which takes variable arguments, something like the following
int log_data (LOG_TYPE eType, ...)
{
/** some logging related stuff here **/
}
In the header file, I use something like
#ifdef LOGGING_ENABLED
int log_data (int nType, ...);
#else
#define log_data(_x_, ...)
#endif
Basically, the idea is to SWITCH debugging ON & OFF ~~~
Problem:
The above logic works perfectly fine in Linux & gcc, but errors outs during compilation in Windows VC++.

Answer 1

Variadic macros are relatively new, for example: this reference says that "Support for variadic macros was introduced in Visual C++ 2005." You might have an older version.
Edit: you are declaring log_data if you want debugging, and not if you don't. This means that you have the definition of the function in an #ifdef as well. As long as you're doing this, a solution would be:
int log_data (int nType, ...)
{
#ifdef LOGGING_ENABLED
/* the code to do logging */
#else
return 0; /* or whatever */
#endif
}
and in your header file, declare the function as usual:
int log_data (int nType, ...);
This has a disadvantage that the function call exists even when you're not logging, but the advantage is that it will work without preprocessor support for varargs.

Answer 2

Older versions of VC++ do not support variable arguments in macros.
You can use this trick to get around it:
#ifdef LOGGING_ENABLED
#define log_data log_data_impl
#else
#define log_data
#endif
// usage:
log_data(level, ...)
UPDATE - Another possible workaround:
#ifdef LOGGING_ENABLED
#define log_data(P) log_data_impl P // no braces around P!
#else
#define log_data(P)
#endif
// usage: we have to use two braces
log_data((level, ...));