Factory patterns in library code

Hello.

I encountered a problem when I wrote a library with a factory-pattern
(with Visual C++ 2008 in Windows).

Sample code here (Two projects):

-------------------------------------------------------------
Project1 (factory_test.exe)
-------------------------------------------------------------

==== main.cpp ===============================================

#include <iostream>
#include <factory_lib.hpp>

int main()
{
     dummy_1(); // If comment out this line, "item_1" do not
registered.
     //dummy_2();
     std::cout << "count = " << item_factory::get_instance().count() <<
std::endl;

     if (item_base *p = item_factory::get_instance().get(1)) {
         std::cout << p->test() << std::endl;
     }
     else {
         std::cout << "(NULL)" << std::endl;
     }

     return 0;
}

-------------------------------------------------------------
Project2 (factory_lib.lib)
-------------------------------------------------------------

=== factory_lib.hpp =========================================

#ifndef __FACTORY_LIB_HPP__
#define __FACTORY_LIB_HPP__

#include <map>

struct item_base
{
     virtual ~item_base() {}
     virtual const char *test() const { return "item_base"; }
};

class item_factory
{
     std::map<int, item_base*> m;

public:
     static item_factory& get_instance()
     {
         static item_factory instance;
         return instance;
     }

     // Count registered items.
     size_t count()
     {
         return m.size();
     }

     // Get a registered item specified by ID.
     item_base *get(int id)
     {
         std::map<int, item_base*>::iterator ite = m.find(id);
         if (ite != m.end()) {
             return ite->second;
         }
         else {
             return 0;
         }
     }

     // Register a item with ID.
     void set(int id, item_base* item)
     {
         m[id] = item;
     }
};

struct item_registrar
{
     item_registrar(int item_id, item_base* item)
     {
         item_factory::get_instance().set(item_id, item);
     }
};

void dummy_1();
void dummy_2();

#endif

=== item_1.cpp ============================================

#include "factory_lib.hpp"

void dummy_1() {}

struct item_1 : public item_base
{
     virtual const char *test() const { return "item_1"; }
};

static item_registrar reg(1, new item_1);

=== item_2.cpp ============================================

#include "factory_lib.hpp"

void dummy_2() {}

struct item_2 : public item_base
{
     virtual const char *test() const { return "item_2"; }
};

static item_registrar reg(2, new item_2);

There are two prejects. "factory_test.exe" is main executable project,
and "factory_lib.lib" is a static-linked library project.
The item_factory class has a map container hold pairs of item-ID and a
pointer to item derived from item_base class.
Two objects of item_1 and item_2 should be automatically registered
into item_factory in constructor of item_registrar class when this
application was initialized.

But if I removed dummy_1() and dummy_2() functions, no item
registered.
I know why. (Because there are no reference from main.cpp to
item_1.cpp and item_2.cpp)

Are there any recommended solution in a platform-independent way or
any library ?

I think this is maybe a common implementation problem of factory
patterns in library code.

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