Re: A simple reference variable question

From:

"John Carson" <jcarson_n_o_sp_am_@netspace.net.au>

Newsgroups:

microsoft.public.vc.language

Date:

Sun, 12 Nov 2006 15:50:14 +1100

Message-ID:

<#z6fmYhBHHA.4808@TK2MSFTNGP03.phx.gbl>

"John Carson" <jcarson_n_o_sp_am_@netspace.net.au> wrote in message
news:%23AaFS$gBHHA.3604@TK2MSFTNGP03.phx.gbl

"Ray Mitchell" <RayMitchell_NOSPAM_@MeanOldTeacher.com> wrote in
message news:CF156B0B-2063-4CE3-BF44-1056E921E794@microsoft.com

"Igor Tandetnik" wrote:

"Ray Mitchell" <RayMitchell_NOSPAM_@MeanOldTeacher.com> wrote in
message news:5AA7F20A-917A-4833-8619-8F62E71F903A@microsoft.com

In the following code I got a compile error on the declaration of
r1 because, obviously, it is not initialized. However, I kind of
expected to get a link error on the declaration of r2, but I
didn't. Could someone please explain why there is no error?

You never use it, so the compiler never asks the linker to look for
it. --
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going
to land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

Okay, but if I remove the initializer from r1 I do get a compiler
error, although I never use it either. I guess I'm still missing the
point.

You have to use something to get a linker error. You may not have to
use something to get a compiler error.

Just to be quite clear: an uninitialized extern reference declaration is
perfectly legal from the compiler's point of view even if you *do* use it,
e.g.,

int main()
{
    extern int &r2;
    r2 += 5;

   return 0;
}

will compile without a problem. Initialization is required for the
*definition* of the reference, not for extern *declarations* of the
reference.

However, using r2 means that the linker will look for a properly initialized
reference elsewhere in the project. Not using it means that the linker
won't.

--
John Carson