Re: Reference to void

"James Kanze" <>
26 Oct 2006 10:37:37 -0400
Greg Herlihy wrote:

Lucian Radu Teodorescu wrote:

{ 8.3.2/1 prohibits declarations of references to void. -mod }

Is the following code valid?

int i = 5;
void* pv = &i;
void& rv = *pv; // Error here on VC 2005

If not, why isn't it valid?

For the same reason it is not legal to declare a variable with a void
type or to dereference a void pointer - "void" in C and C++ denotes
either that the type is not known (as in the case of a void pointer) or
there is no type at all (as in the case of a function returning void).

Just a nit, but formally, the situation is a bit more
complicated. Like static, the keyword void is overloaded in
C++. As a type, it's an incomplete type which cannot be
completed. Since it cannot be completed, no objects of the type
can exist, and since a reference must be initialized to
designate an actual object, it makes no sense to allow
references to void. (That's formally, of course. Colloquially,
your statement that it's an unknown type is probably closer to
the way it is used.) As the return value of a function, it's
not really a type; it just says that the function doesn't return
anything. And as the single parameter type of a function, it
says that the function takes no arguments, despite the fact that
one has been declared. (Of course, in C++, we don't use this,
but C programmers do.)

James Kanze (GABI Software)
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