> Yeah, but the problem is, if some M<N is not referred to by the
> format, you can't know what type to pass to va_arg to skip over it
> to get to argument N.

I was curious about this, so I looked it up in the Single Unix Spec.
Such a format string is not legal; you have to use all of the
arguments up to the highest one you use.

This struck me as pretty error-prone, but there you have it.  I hope
that common implementations don't try to compensate for programmers
who screw up.