Singleton MFC Extension DLL

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From: MFDonadeli on 7 Jan 2010 12:54

---

Hi.

I declare a singleton on a MFC extension DLL, like this:

<pre>
//header file: SingleTon.h
class AFX_EXT_CLASS CMySingleton
{
public:
static CMySingleton* Instance()
{
if(!singleton)
singleton = new CMySingleton();
return singleton;
}

int a;

// Other non-static member functions
private:
CMySingleton() {}; // Private
constructor
CMySingleton(const CMySingleton&); // Prevent copy-
construction
CMySingleton& operator=(const CMySingleton&); // Prevent
assignment
virtual ~CMySingleton() {};

static CMySingleton* singleton;
};

And in a cpp file I code the following line:

CMySingleton* CMySingleton::singleton = NULL;
</pre>

Code 2:
<pre>
CMySingleton *a;

a = CMySingleton::Instance();
</pre>

The problem is when I code "code 2" in a Regular Dll, all works fine,
but when I code "code 2" in another MFC extension DLL gives an error:

<pre>
unresolved external symbol "private: static class CMySingleton*
CMySingleton::singleton" (?singleton(a)CMySingleton@@0PAV1@A)
</pre>

Any idea?

From: Ajay Kalra on 7 Jan 2010 13:01

---

On Jan 7, 12:54 pm, MFDonadeli <mfdonad...(a)gmail.com> wrote:
> Hi.
>
> I declare a singleton on a MFC extension DLL, like this:
>
> <pre>
> //header file: SingleTon.h
> class AFX_EXT_CLASS CMySingleton
> {
> public:
>   static CMySingleton* Instance()
>   {
>         if(!singleton)
>                 singleton = new CMySingleton();
>     return singleton;
>   }
>
>   int a;
>
> // Other non-static member functions
> private:
>   CMySingleton() {};                                 // Private
> constructor
>   CMySingleton(const CMySingleton&);                 // Prevent copy-
> construction
>   CMySingleton& operator=(const CMySingleton&);      // Prevent
> assignment
>   virtual ~CMySingleton() {};
>
>   static CMySingleton* singleton;
>
> };
>
> And in a cpp file I code the following line:
>
> CMySingleton* CMySingleton::singleton = NULL;
> </pre>
>
> Code 2:
> <pre>
> CMySingleton *a;
>
> a = CMySingleton::Instance();
> </pre>
>
> The problem is when I code "code 2" in a Regular Dll, all works fine,
> but when I code "code 2" in another MFC extension DLL gives an error:
>
> <pre>
> unresolved external symbol "private: static class CMySingleton*
> CMySingleton::singleton" (?singleton(a)CMySingleton@@0PAV1@A)
> </pre>
>
> Any idea?

Are you sure you are including the correct .lib file in MFC extesion
DLL where you code2 sits?

--
Ajay

From: MFDonadeli on 7 Jan 2010 13:05

---

On 7 jan, 16:01, Ajay Kalra <ajayka...(a)yahoo.com> wrote:
> On Jan 7, 12:54 pm, MFDonadeli <mfdonad...(a)gmail.com> wrote:
>
>
>
>
>
> > Hi.
>
> > I declare a singleton on a MFC extension DLL, like this:
>
> > <pre>
> > //header file: SingleTon.h
> > class AFX_EXT_CLASS CMySingleton
> > {
> > public:
> >   static CMySingleton* Instance()
> >   {
> >         if(!singleton)
> >                 singleton = new CMySingleton();
> >     return singleton;
> >   }
>
> >   int a;
>
> > // Other non-static member functions
> > private:
> >   CMySingleton() {};                                 // Private
> > constructor
> >   CMySingleton(const CMySingleton&);                 // Prevent copy-
> > construction
> >   CMySingleton& operator=(const CMySingleton&);      // Prevent
> > assignment
> >   virtual ~CMySingleton() {};
>
> >   static CMySingleton* singleton;
>
> > };
>
> > And in a cpp file I code the following line:
>
> > CMySingleton* CMySingleton::singleton = NULL;
> > </pre>
>
> > Code 2:
> > <pre>
> > CMySingleton *a;
>
> > a = CMySingleton::Instance();
> > </pre>
>
> > The problem is when I code "code 2" in a Regular Dll, all works fine,
> > but when I code "code 2" in another MFC extension DLL gives an error:
>
> > <pre>
> > unresolved external symbol "private: static class CMySingleton*
> > CMySingleton::singleton" (?singleton(a)CMySingleton@@0PAV1@A)
> > </pre>
>
> > Any idea?
>
> Are you sure you are including the correct .lib file in MFC extesion
> DLL where you code2 sits?
>
> --
> Ajay

Yes, via Project Dependencies on VS 2008...

From: Joseph M. Newcomer on 7 Jan 2010 13:24

---

Project Dependencies only indicates DEPENDENCIES. In no way, ever, under any imaginable
scenario, does it actually do anything that would cause the linker to see the .lib file
that is used. You must explicitly add that .lib file to the linker command line.

The only thing Dependencies guarantees is that the DLL will be rebuilt before the main
executable. Absolutely nothing more than that is conveyed by the concept of "dependency".
joe

On Thu, 7 Jan 2010 10:05:18 -0800 (PST), MFDonadeli <mfdonadeli(a)gmail.com> wrote:

>On 7 jan, 16:01, Ajay Kalra <ajayka...(a)yahoo.com> wrote:
>> On Jan 7, 12:54�pm, MFDonadeli <mfdonad...(a)gmail.com> wrote:
>>
>>
>>
>>
>>
>> > Hi.
>>
>> > I declare a singleton on a MFC extension DLL, like this:
>>
>> > <pre>
>> > //header file: SingleTon.h
>> > class AFX_EXT_CLASS CMySingleton
>> > {
>> > public:
>> > � static CMySingleton* Instance()
>> > � {
>> > � � � � if(!singleton)
>> > � � � � � � � � singleton = new CMySingleton();
>> > � � return singleton;
>> > � }
>>
>> > � int a;
>>
>> > // Other non-static member functions
>> > private:
>> > � CMySingleton() {}; � � � � � � � � � � � � � � � � // Private
>> > constructor
>> > � CMySingleton(const CMySingleton&); � � � � � � � � // Prevent copy-
>> > construction
>> > � CMySingleton& operator=(const CMySingleton&); � � �// Prevent
>> > assignment
>> > � virtual ~CMySingleton() {};
>>
>> > � static CMySingleton* singleton;
>>
>> > };
>>
>> > And in a cpp file I code the following line:
>>
>> > CMySingleton* CMySingleton::singleton = NULL;
>> > </pre>
>>
>> > Code 2:
>> > <pre>
>> > CMySingleton *a;
>>
>> > a = CMySingleton::Instance();
>> > </pre>
>>
>> > The problem is when I code "code 2" in a Regular Dll, all works fine,
>> > but when I code "code 2" in another MFC extension DLL gives an error:
>>
>> > <pre>
>> > unresolved external symbol "private: static class CMySingleton*
>> > CMySingleton::singleton" (?singleton(a)CMySingleton@@0PAV1@A)
>> > </pre>
>>
>> > Any idea?
>>
>> Are you sure you are including the correct .lib file in MFC extesion
>> DLL where you code2 sits?
>>
>> --
>> Ajay
>
>Yes, via Project Dependencies on VS 2008...
Joseph M. Newcomer [MVP]
email: newcomer(a)flounder.com
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm

From: Ajay Kalra on 7 Jan 2010 13:26

---

On Jan 7, 1:05 pm, MFDonadeli <mfdonad...(a)gmail.com> wrote:
> On 7 jan, 16:01, Ajay Kalra <ajayka...(a)yahoo.com> wrote:
>
>
>
> > On Jan 7, 12:54 pm, MFDonadeli <mfdonad...(a)gmail.com> wrote:
>
> > > Hi.
>
> > > I declare a singleton on a MFC extension DLL, like this:
>
> > > <pre>
> > > //header file: SingleTon.h
> > > class AFX_EXT_CLASS CMySingleton
> > > {
> > > public:
> > >   static CMySingleton* Instance()
> > >   {
> > >         if(!singleton)
> > >                 singleton = new CMySingleton();
> > >     return singleton;
> > >   }
>
> > >   int a;
>
> > > // Other non-static member functions
> > > private:
> > >   CMySingleton() {};                                 // Private
> > > constructor
> > >   CMySingleton(const CMySingleton&);                 // Prevent copy-
> > > construction
> > >   CMySingleton& operator=(const CMySingleton&);      // Prevent
> > > assignment
> > >   virtual ~CMySingleton() {};
>
> > >   static CMySingleton* singleton;
>
> > > };
>
> > > And in a cpp file I code the following line:
>
> > > CMySingleton* CMySingleton::singleton = NULL;
> > > </pre>
>
> > > Code 2:
> > > <pre>
> > > CMySingleton *a;
>
> > > a = CMySingleton::Instance();
> > > </pre>
>
> > > The problem is when I code "code 2" in a Regular Dll, all works fine,
> > > but when I code "code 2" in another MFC extension DLL gives an error:
>
> > > <pre>
> > > unresolved external symbol "private: static class CMySingleton*
> > > CMySingleton::singleton" (?singleton(a)CMySingleton@@0PAV1@A)
> > > </pre>
>
> > > Any idea?
>
> > Are you sure you are including the correct .lib file in MFC extesion
> > DLL where you code2 sits?
>
> > --
> > Ajay
>
> Yes, via Project Dependencies on VS 2008...

As Joe already pointed out, it doesnt mean much in your case. All you
are ensuring is the build order as such. You need to somehow link to
the library you are trying to use.

How did this work for the Regular DLL for you? You would have the same
problem there as well.

--
Ajay

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