Macro auto-injecting argument without VARIADIC support - c++

Question

I have a macro with varargs that auto injects some arguments, like the first below injecting the argument "__FNAME__":
#ifdef VERBOSE
#define logdbg(format, ...) debugff(__FNAME__, format, ##__VA_ARGS__)
#elif defined(NORMAL)
#define logdbg(format, ...) debugf(format, ##__VA_ARGS__)
#else
#define logdbg(format, ...) /* debud off */
#endif
But I need to keep this macro working with compilers without MACRO VARIADIC support (in SCO Unix and AIX 4.3 Copmiler v3).
In these environments I have now:
#ifdef VERBOSE
#define logdbg debugff(__FNAME__, format, ##__VA_ARGS__)
#elif defined(NORMAL)
#define logdbg debugf
#else
#define logdbg if(1);else debugf
#endif
These compilers didn't accepted the comment in the last macro definition, and I get the if(1);else blablabla that works fine from https://stackoverflow.com/a/687412/926064
But I need yet a solution to the first case, where an argument is "injected" by macro.
Some workaround to do that ?
EDIT:
As it isn't a software with multithread support, I'm thinking to change the debug 'framework' to inject the arguments using side functions to set values in 'context' variables (global, static, etc):
#define logdbg pass_args(__FNAME__); debugf
More possibles workarounds ?

Answer 1

Assuming it is impossible to use a different compiler (which seems a dubious requirement, but let's put that aside), for certain, you will need a different function for logdbg to expand into. Probably, that function would take the __FNAME__ argument from another source, like a global variable.
#define logdbg ((logdbg_fname__ = __FNAME__), debugff_broken)
void debugff_broken(const char *fmt, ...) {
extern const char *logdbg_fname__;
va_list ap;
va_start(ap, fmt);
vdebugff(logdbg_fname__, fmt, ap);
va_end(ap);
}
Where vdebugff is like debugff except it takes a va_list.
If thread safety is required, use thread specific storage instead of a common global.