Problem with static variable definitions

Hi

I'm trying to implement a template based factory, following the
guidelines of the following article:
http://www.codeproject.com/KB/architecture/all_kinds_of_factories.aspx
(I'm trying Factory 6: the template-factory).

I get it to work fine, but as soon as I define more than 1 static
factory, each one in a different class, I get the following error:

Creating library file: bin\libQtilities.a
../tmp\Logger.o: In function
`ZN9Qtilities24AbstractFormattingEngineD1Ev':
D:/ScinericSoftware/Products/Qtilities/trunk/include/Qtilities/
AbstractFormattingEngine.h:(.bss+0x8): multiple definition of
`Qtilities::FileLoggerEngine::factory'
../tmp\FileLoggerEngine.o:c:/Tools/Qt/2009.02/qt/include/QtCore/../../
src/corelib/tools/qstring.h:(.bss+0x0): first defined here
collect2: ld returned 1 exit status

Below is some code to show exactly what I'm doing:

    //! Factory interface which is used by factories to create
instances of registered class types.
    /*!
    */
    template <class BaseClass>
    class FactoryInterface
       {
       public:
          FactoryInterface() {}
          virtual ~FactoryInterface() {}
          virtual BaseClass *createInstance() = 0;
          virtual QString getTag() = 0;
       };

    //! Factory item class which is used inside classes which can
register themselves as items in factories.
    /*!
    */
    template <class BaseClass,class ActualClass>
    class FactoryItem : public FactoryInterface<BaseClass>
       {
       public:
          FactoryItem() { tag = QString("");}
          virtual ~FactoryItem() {}
          virtual BaseClass *createInstance() {return new
ActualClass;}
          QString getTag() { return tag; }
          bool setTag(const QString& iface_tag) {
              if (tag == QString("")) {
                  tag = iface_tag;
                  return true;
              } else
                  return false;
          }
       private:
          QString tag;
       };

    //! A factory class which can produce class instances through
registered factory interfaces.
    /*!
    */
    template <class BaseClass>
    class Factory
       {
       public:
          Factory() {}
          ~Factory() {}

          void registerFactoryInterface(FactoryInterface<BaseClass>*
interface) {
              if (interface->getTag() != QString(""))
                reg_ifaces[interface->getTag()] = interface;
          }
          void unregisterFactoryInterface(const QString& tag)
{ reg_ifaces.remove(tag); }
          QStringList registeredTags() { return reg_ifaces.keys(); }
          bool isTagValid(const QString& tag) { return
reg_ifaces.contains(tag); }
          BaseClass* createInstance(const QString& tag) {
              if (isTagValid(tag))
                  return reg_ifaces.value(tag)->createInstance();
              else
                  return 0;
          }

       private:
          QMap<QString,FactoryInterface<BaseClass>* > reg_ifaces;
       };

I then create classes with static FactoryItem factories in them as
shown below:

    class FormattingEngine_Default : virtual public
AbstractFormattingEngine
    {
    public:
        FormattingEngine_Default() : AbstractFormattingEngine() {
            factory_item.setTag("Default");
        }
        ~FormattingEngine_Default() {}

        static FactoryItem<AbstractFormattingEngine,
FormattingEngine_Default> factory_item;

    };
    FactoryItem<AbstractFormattingEngine, FormattingEngine_Default>
FormattingEngine_Default::factory_item;

And another class like this:

    class QTILITIES_SHARED_EXPORT FileLoggerEngine : virtual public
AbstractLoggerEngine
    {

    public:
        FileLoggerEngine();
        ~FileLoggerEngine();

        // Make this class a factory item
        static FactoryItem<AbstractLoggerEngine, FileLoggerEngine>
factory;
    };
    FactoryItem<AbstractLoggerEngine, FileLoggerEngine>
FileLoggerEngine::factory;

If needed I can post the base classes as well. I hope I posted
everything that is necessary. To be honest, I wondered why the
FileLoggerEngine::factory variable needs to be defined outside the
class definition while I was reading the article, and now this gives
the problem.

Any ideas on why I get this error will be greatly appreciated.

Thanks in advance,
Jaco