null pointers

null pointers

Because it's not a matter of narrow vs. wide, or using something "narrower than (void *)". If the function specification says "This vararg list is terminated by null character pointer", then, by the standard, you have to pass something equivalent to "(char *) 0", and "(void *) 0" isn't. The idea of a "void *" being generic is that variables of type "void *" can store pointers of any type, and pointers can be cast to void and then back to the original type without information loss. But they are a distinct type, and not necessarily interchangeable with other pointer types.

Does this matter the vast majority of the time? No. Is it C standard lawyer nitpickery of the most annoying kind? Yes, of course. But the C89 standard is this way precisely because there were some systems for which this kind of nitpicking *did* matter.

But yes, where you wrote: "It seems to me that (type *) NULL is still a perfectly good choice of value for such a parameter." is correct. I should have distinguished that in my original reply.

"The idea of a "void *" being generic is that variables of type "void *" can store pointers of
any type, and pointers can be cast to void and then back to the original type without
information loss."

As far as I remember it is illegal to convert between void* and any function pointer type in
ANSI C; POSIX' specification of dlsym() actually relies on what is essentially a vendor
extension to work for function pointers.

This is surely related to the aliasing rules, which also have a similar 
special hole allowing aliasing of of void * and char *, but not of 
pointers of any other distinct types.