getting error LNK2019 when i use std::auto_ptr - c++

Question

i ahve a class named FiniteStateMachine declared as below
header file : FiniteStateMachine.h
class FiniteStateMachine
{
public:
//Constructor
FiniteStateMachine();
//Destructor
~FiniteStateMachine();
}
source file : FiniteStateMachine.cpp
////////////////////////////////////////////////////////////////////////
// Constructor
////////////////////////////////////////////////////////////////////////
FiniteStateMachine::FiniteStateMachine()
:m_InitialState("")
,m_CurrentState(NULL)
,m_Running(false)
{
RegisterBaseTypes();
}
////////////////////////////////////////////////////////////////////////
// Destructor
////////////////////////////////////////////////////////////////////////
FiniteStateMachine::~FiniteStateMachine()
{
if (m_Running) Stop();
Clear();
}
and ihave a heade file named FSM that i collect all class of project in it
FSM.H
class ICORE_API FiniteStateMachine;
ok i compile it and now wanna to use this class in another library.
every thing about linking that library has been done.
in the client class when i use FiniteStateMachine with auto_ptr i get linker error :
#include "FSM.H"
std::auto_ptr<FiniteStateMachine > fsm;
error LNK2019: unresolved external symbol "public: __thiscall IFSM::FiniteStateMachine::~FiniteStateMachine(void)" (??1FiniteStateMachine#IFSM##QAE#XZ) referenced in function "public: void * __thiscall FSM::FiniteStateMachine::`scalar deleting destructor'(unsigned int)" (??_GFiniteStateMachine#IFSM##QAEPAXI#Z)
but by declaring such as this
#include FSM.h
FiniteStateMachine* fsm;
every thing is ok and project completely compiled.
now i want to know why this happen? what is wrong here.

Answer 1

The std::auto_ptr<> generates the code to call the FiniteStateMachine's destructor and in your case you don't provide it, because you only provide by giving the forward declaration.