Using a static variable in an abstract base class - c++

Question

I am trying to create a state machine. I have created a class called BaseState that all states inherits from. The problem I'm having is that when the sub classes change a BaseState member variable, it does not change the variable for all of the inherited classes. From what I know of programming, this is when I use static. But in my case I get a linker error (LNK2001).
So when I call ChangeState(State::MenuState); inside SplashState, it switches, but switches back since the value in BaseState has not changed.
class StateMachine
{
private:
State _currentState;
std::vector<BaseState*> _baseStates;
void ProcessStateRequest();
public:
StateMachine(InitVar initVar);
~StateMachine();
void Update(float deltaTime);
};
That adds the states like this:
StateMachine::StateMachine(InitVar initVar)
{
_currentState = State::SPLASHSTATE;
for (int i = 0; i < State::EXITSTATE; i++)
{
switch (i)
{
case SPLASHSTATE:
{
_baseStates.push_back(new SplashState(initVar));
break;
}
case MENUSTATE:
{
_baseStates.push_back(new MenuState(initVar));
break;
}
case PLAYSTATE:
{
_baseStates.push_back(new PlayState(initVar));
break;
}
case OPTIONSSTATE:
{
_baseStates.push_back(new OptionsState(initVar));
break;
}
}
}
}
With changing states like this:
void StateMachine::ProcessStateRequest()
{
//if currentState does not match with the new requested state.
if (_currentState != _baseStates[_currentState]->GetNewStateRequest())
{
_baseStates[_currentState]->OnStateExit();
_currentState = _baseStates[_currentState]->GetNewStateRequest();
_baseStates[_currentState]->OnStateEnter();
}
}
Inside basestate.h:
enum State
{
SPLASHSTATE,
MENUSTATE,
PLAYSTATE,
OPTIONSSTATE,
EXITSTATE,
};
class BaseState
{
private:
State _newStateRequest; //Cannot edit this from subclasses. Adding static causes linker error.
protected:
ObjectHandler* _objectHandler;
UIHandler* _uiHandler;
void ChangeState(State newState);
public:
BaseState(InitVar initVar);
~BaseState();
virtual void Update(float deltaTime) = 0;
virtual void OnStateEnter() = 0;
virtual void OnStateExit() = 0;
State GetNewStateRequest()const;
};
The last part of basestate.cpp:
BaseState::BaseState(InitVar initVar)
{
_objectHandler = initVar.objectHandler;
_uiHandler = initVar.uiHandler;
_newStateRequest = SPLASHSTATE;
}
BaseState::~BaseState()
{}
void BaseState::ChangeState(State newState)
{
_newStateRequest = newState;
}
State BaseState::GetNewStateRequest() const
{
return _newStateRequest;
}

Answer 1

MikeCAT in comments gave this answer. Problem solved by doing this;
class BaseState
{
private:
static State BaseState::_newStateRequest;
//State _newStateRequest;
and
#include "BaseState.h"
State BaseState::_newStateRequest;
BaseState::BaseState(InitVar initVar)