设计模式-State(行为模式)-很好的实现了对象的状态逻辑与动作实现的分类，状态逻辑在State的派生类实现，动作可以放在Context类中实现。

以下代码来源： 设计模式精解－GoF 23种设计模式解析附C++实现源码

//Context.h

#pragma once
class State;
class Context
{
public:
    Context();
    Context(State* st);
    virtual ~Context();
    void OperationInference();
    void OperationChangeState();
protected:
private:
    friend class State;
    bool changeState(State* st);
    State* _state;
};

//Context.cpp

#include"Context.h"
#include"State.h"
 
Context::Context() {}
Context::Context(State* st)
{
    this->_state = st;
}
Context::~Context()
{
    delete _state;
}
void Context::OperationInference()
{
    _state->OperationInference(this);
}
bool Context::changeState(State* state)
{
    this->_state = state;
    return true;
}
void Context::OperationChangeState()
{
    _state->OperationChangemode(this);
}

//State.h

#pragma once
class Context;
class State
{
public:
    State();
    virtual ~State();
    virtual void OperationInference(Context*) = ;
    virtual void OperationChangemode(Context*) = ;
protected:
    bool changeState(Context* con, State* st);
private:
};
 
class ConcreateStateA:public State
{
public:
    ConcreateStateA();
    virtual ~ConcreateStateA();
    virtual void OperationInference(Context*);
    virtual void OperationChangemode(Context*);
private:
protected:
};
 
class ConcreateStateB :public State
{
public:
    ConcreateStateB();
    virtual ~ConcreateStateB();
    virtual void OperationInference(Context*);
    virtual void OperationChangemode(Context*);
private:
protected:
};

//State.cpp

#include"State.h"
#include"context.h"
#include<iostream>
State::State(){}
State::~State(){}
void State::OperationInference(Context* con)
{
    std::cout << "State::..." << std::endl;
}
bool State::changeState(Context* con, State* st)
{
    con->changeState(st);
    return true;
}
void State::OperationChangemode(Context* con)
{
 
}
ConcreateStateA::ConcreateStateA()
{
 
}
ConcreateStateA::~ConcreateStateA()
{}
void ConcreateStateA::OperationInference(Context* con)
{
    std::cout << "OperationInference ConcreateStateA" << std::endl;
}
void ConcreateStateA::OperationChangemode(Context* con)
{
    OperationInference(con);
    this->changeState(con, new ConcreateStateB());
}
ConcreateStateB::ConcreateStateB(){}
ConcreateStateB::~ConcreateStateB(){}
void ConcreateStateB::OperationInference(Context* con)
{
    std::cout << "OperationInference ConcreateStateB" << std::endl;
}
void ConcreateStateB::OperationChangemode(Context* con)
{
    OperationInference(con);
    this->changeState(con, new ConcreateStateA());
}

//main.cpp

#include"Context.h"
#include"State.h"
#include<iostream>
int main(int args, char* argv)
{
    State* st = new ConcreateStateA();
    Context* con = new Context(st);
    con->OperationChangeState();
    con->OperationChangeState();
    con->OperationChangeState();
    if (!con)
        delete con;
    if (NULL != st)
        st = NULL;
    return ;
 
}