Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sources.redhat.com/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com
Message-ID: <3FB7C911.5030203@jon-foster.co.uk>
Date: Sun, 16 Nov 2003 18:59:29 +0000
From: Jon Foster <jon AT jon-foster DOT co DOT uk>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4) Gecko/20030624
X-Accept-Language: en-gb, en
MIME-Version: 1.0
To: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: Exporting const variables from DLLs (GCC bug?)
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-Virus-Scanned: by amavisd-new at eclipse.net.uk

Hi,

Given this source code:
> extern const int meaning_of_life __declspec(dllexport);
> const int meaning_of_life __declspec(dllexport) = 42;

GCC complains:
> $ c++ -g -O2 -c test.cxx -o test.o
> test.cxx:2: error: external linkage required for symbol 'const int
>    meaning_of_life' because of 'dllexport' attribute.

However, it compiles successfully with the "const" qualifier
removed:
> extern int meaning_of_life __declspec(dllexport);
> int meaning_of_life __declspec(dllexport) = 42;

Why does adding the "const" qualifier change this?  Is
this a known limitation of DLLs?  If so, the error message
is a little confusing.  If not, then this is a GCC bug.

Removing the explicit "extern" line has no effect in either
case.

My Cygwin installation was updated recently - I'm using the
standard Cygwin GCC 3.3.1-3 package:
> $ c++ --version
> c++ (GCC) 3.3.1 (cygming special)

If you want any more info, just ask.

Incidentally, this bug affects src/sid/component/ in the
Cygwin CVS tree.  I'd prepared this minimal test case before
I realized that this subdirectory isn't needed to build the
Cygwin DLL.  (Doh!  CVS doing unexpected things strikes again).

Kind regards,

Jon Foster





--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/