Re: References static in header files

From:
Alberto Ganesh Barbati <AlbertoBarbati@libero.it>
Newsgroups:
comp.lang.c++.moderated
Date:
Wed, 17 Sep 2008 16:28:58 CST
Message-ID:
<7h9Ak.152829$FR.437030@twister1.libero.it>
Dave the Funkatron ha scritto:

Hey all,

Suppose I have a value somewhere, declared in a header like so:

   int someValue;

then defined in a cpp file like so:

   int someValue = 9;

That all compiles nicely.


Really? That surprises me. You are openly violating the ODR because "int
somevalue;" is a *definition*, not a declaration, so you have multiple
definitions of the same object. The program is ill-formed and the only
thing that may make such a program work is a blasphemy called "tentative
definitions" that is allowed by C but it's forbidden in C++. Probably
you are using GCC in such a way that tentative definitions are allowed
in C++.

To make your program well-formed you *must* use extern keyword in the
header file.

That all compiles nicely. However, if that variable were a reference
to an int, it wouldn't work so well. If I merely declare it in the
header like this:

   int& someOtherValue;

I get an error from GCC saying

   test.h:13: error: 'someOtherValue' declared as reference but not
initialized

However, if I define the value in the header like this:

   int& someOtherValue = someValue;

I run into problems at link-time if I include that header from
multiple cpp files. I also tried

   extern int& someOtherValue;

just for kicks, but no go. Any ideas on how to get around this would
be appreciated.


As another poster already remarked, there must be a better way to
achieve what you want (which is not clear from your words) that would
avoid the use of a global reference.

Anyway, if you can't redesign you application, the quickest way is to
use a pointer instead of a reference.

HTH,

Ganesh

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