Re: Static members of a class in a dll

From:

Cholo Lennon <chololennon@hotmail.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 27 Sep 2010 14:27:22 -0300

Message-ID:

<i7qk5m$76r$2@speranza.aioe.org>

On 24/09/2010 08:13, Josemi wrote:

On 23 sep, 18:15, Joseph M. Newcomer<newco...@flounder.com> wrote:

Grnerally, you should not be exporting variables from a DLL. You should probably export
state setter/getter methods instead. THere are a number of things that can go wrong here
because of how DLLs work, and I would avoid them entirely by never, ever, making a static
int a public member. Make it a protected member, and add void SetValor(int) and int
GetValor() methods. And I don't want to hear anything about "efficiency" here; it is
completely and utterly irrelevant to the discussion.
joe

On Thu, 23 Sep 2010 02:49:23 -0700 (PDT), Josemi<josemiant...@gmail.com> wrote:

Hello!

I have a curious case with a class that has a static member defined in
a DLL. Let me explain:

dll.h
class __declspec (dllexport) A
{
   public:static int valor;
   PrintOut ()
   {
      TRACE1(valor);
   }
}

Your code correctly exports the class, but doesn't import it. You need a
macro to achieve this (in order to be 'correctly' consumed by a client):

#ifdef TESTDLL_EXPORTS
#define TESTDLL_API __declspec(dllexport)
#else
#define TESTDLL_API __declspec(dllimport)
#endif

class TESTDLL_API A { ... };

Just define TESTDLL_EXPORTS in your DLL project.

dll.cpp
A::valor=23;

main.h
class B:A
{
}

main.cpp
A::valor;
{
   A objeto;

   objeto.valor = 34;
   objeto.PrintOut();
}

Well, it happens that the value given in "main.cpp" objeto.valor =
34, PrintOut print 23. Can you know what is wrong? although I have
some idea, I think the problem is that I have to declare A::valor in
the two routines and well, the compiler creates two instances of
A::valor, Is it posible declare only one in dll.cpp file? or any idea
how to solve this problem. I can think of set routines that fill this
gap, but I wanted something less complicated.

Thanks in advance

your sincerely
Josemi

Joseph M. Newcomer [MVP]
email: newco...@flounder.com
Web:http://www.flounder.com
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Many thanks for your help, Joe.

I was waiting for your comment because You are usually whom help to
everyone.
Thank you very much for everything, truly and wholeheartedly

Regards

--
Cholo Lennon
Bs.As.
ARG