编译问题，类之间相互引用。
windows 下没问题，Linux 下一直没解决啊！
程序框架如下：　

/**
*文件名:MessageFactory.h
**/
#ifndef MessageFactory_h
#define MessageFactory_h

#include "MessageServer.h "

class MessageServer ;

class MessageFactory
{
public:
MessageFactory(void){}

virtual ~MessageFactory(void){}

virtual void CreateReceiver(int code, MessageServer* server) = 0;
};

#endif


/**
*文件名:MessageFactoryImpl.h
**/
#ifndef MessageFactoryImpl_h
#define MessageFactoryImpl_h

#include "MessageFactory.h "

class MessageFactoryImpl :public MessageFactory
{

public:
MessageFactoryImpl();
virtual ~MessageFactoryImpl(){}

virtual void CreateReceiver(int code, MessageServer* server);
};
#endif

/**
*文件名:MessageFactoryImpl.cpp
**/

#include "MessageFactoryImpl.h "

MessageFactoryImpl::MessageFactoryImpl()
{
}

void MessageFactoryImpl::CreateReceiver(int code, MessageServer* server)
{
}


/**
*文件名:MessageServer.h
**/
#ifndef MessageServer_h
#define MessageServer_h

#include "MessageFactory.h "

class MessageFactory ;

class MessageServer
{
public:
MessageServer();
MessageServer(int udpPort, MessageFactory* factory, long timeout);
virtual ~MessageServer();

};
#endif

/**
*文件名:MessageServer.cpp
**/

#include "MessageServer.h "

MessageServer::MessageServer()
{

}

MessageServer::MessageServer(int udpPort, MessageFactory* factory, long timeout)
{
}

MessageServer::~MessageServer()
{
}

//:test.cpp
#include <iostream>

#include "MessageFactoryImpl.h "
#include "MessageServer.h "

using namespace std;

int main()
{

MessageFactoryImpl *a=new MessageFactoryImpl();

MessageServer *b=new MessageServer();

cout < < "it 's ok " < <endl;

delete a;
delete b;

return 0;
}


# makefile
test: MessageFactoryImpl.o MessageServer.o
g++ test.cpp -o test

MessageFactoryImpl.o: MessageFactoryImpl.h MessageFactory.h \
MessageServer.o
g++ -c MessageFactoryImpl.cpp

MessageServer.o: MessageFactory.h MessageServer.h
g++ -c MessageServer.cpp




[解决办法]
提示报什么错？？
------解决方案--------------------

MessageFactory::MessageFactory(void){}
这个函数的定义呢？？
[解决办法]
Makefile改第3行

# makefile
test: MessageFactoryImpl.o MessageServer.o
g++ test.cpp -o test MessageFactoryImpl.o MessageServer.o

MessageFactoryImpl.o: MessageFactoryImpl.h MessageFactory.h \
MessageServer.o
g++ -c MessageFactoryImpl.cpp

MessageServer.o: MessageFactory.h MessageServer.h
g++ -c MessageServer.cpp