Re: Singleton MFC Extension DLL

"David Ching" <>
Thu, 7 Jan 2010 13:41:38 -0800
"MFDonadeli" <> wrote in message

With project dependencies, I can access all the classes and functions
on this DLL, and in the build line command the lib apper at the end of
the command.

And I think that if project dependencies is wrong the solution that I
describe, wouldn't compile:

Joe and the others are incorrect. Using Project Dependencies *does* in fact
cause a link of the associated .lib file. You _do not_ have to add the .lib
manually to the linker input.

Now your original code:

//header file: SingleTon.h
class AFX_EXT_CLASS CMySingleton
 static CMySingleton* Instance()
singleton = new CMySingleton();
   return singleton;

 int a;

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

 static CMySingleton* singleton;

Well, you are declaring but not defining a (CMySingleton *) with

     static CMySingleton* singleton;

This must have been done in SinglTon.cpp. But the import lib for your DLL
doesn't export it. Hmm... have you checked that the compile options for
your singleton extension DLL has the _AFXDLL and _USRDLL switches set

BTW, what is the "int a"? Is that a typo?

In this case I can access the Singleton if I remove the variable
static CMySingleton* singleton and put on the Instance function like
static CMySingleton* Instance()
     static CMySingleton* singleton;
               singleton = new CMySingleton();
   return singleton;
but the problem in this case, is that this function create another
instance of CMySingleton, even if static singleton var is already

This should work OK if you initialize as follows:

 static CMySingleton* Instance()
      static CMySingleton* singleton = NULL; // <-- must set NULL!!
                singleton = new CMySingleton();
       return singleton;

-- David

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