版本一、get状态指针

#include <iostream>
using namespace std;//前置声明
class Context;//状态
class State{
public://4个状态virtual void toUp   (Context& context){ }virtual void toDown (Context& context){ }virtual void toLeft (Context& context){ }virtual void toRight(Context& context){ }//显示用virtual void print(){}  
};    //Context
class Context{
public:Context(State *st ):st(st){ }void reset( State* st ){     this->st = st;}State* get(){  //获取私有状态指针return st;}~Context(){ delete st; }
private:State* st;
};//具体状态Up
class Up :public State {
public:virtual void print(){cout << "now Up\n";}virtual void toDown(Context& context);
};//具体状态Down
class Down:public State {
public:virtual void print(){cout << "now Down\n";}virtual void toUp(Context& context);
};//
void Up::toDown(Context& context) {context.~Context();context.reset( new Down );    
}
void Down::toUp(Context& context) {context.~Context();context.reset(new Up );    
}int main() 
{Context c(new Up);     //定义对象( c.get() )->print();  //当前状态( c.get() )->toDown(c); // c 转换状态( c.get() )->print();    //转换过的状态return 0;
}

版本二、统一接口

#include <iostream>//前置声明
class Context;//状态
class State{
public://4个状态virtual void toUp   (Context& context){ }virtual void toDown (Context& context){ }virtual void toLeft (Context& context){ }virtual void toRight(Context& context){ }//显示用virtual void print(){}  
};    //Context
class Context{
public:Context(State *st ):st(st){ }void reset( State* st ){     this->st = st;}//统一接口void toUp   (){ st->toUp(*this); }void toDown (){ st->toDown(*this); }void toLeft (){ st->toLeft(*this); }void toRight(){ st->toRight(*this); }void print  (){st->print(); }~Context(){ delete st; }
private:State* st;
};//具体状态Up
class Up :public State {
public:virtual void print(){std:: cout << "now Up\n";}virtual void toDown(Context& context);
};//具体状态Down
class Down:public State {
public:virtual void print(){std:: cout << "now Down\n";}virtual void toUp(Context& context);
};//类外定义
void Up::toDown(Context& context) {context.~Context();context.reset( new Down );    
}
void Down::toUp(Context& context) {context.~Context();context.reset(new Up );    
}int main() 
{Context c(new Up);     //定义对象c.print();  //当前状态c.toDown(); // 转换状态c.print();  //转换过的状态return 0;
}

版本三、成员函数指针数组

#include <iostream>//前置声明
class Context;//状态
class State{
public://4个状态virtual void toUp   (Context& context){ }virtual void toDown (Context& context){ }virtual void toLeft (Context& context){ }virtual void toRight(Context& context){ }//成员函数指针数组enum Direction { TOUP,TODOWN,TOLEFT,TORIGHT };typedef void (State::*Action)(Context& context); //Action是可以指向，任何表示方向的成员函数指针static Action Menu[]; //成员函数指针数组//显示用virtual void print(){}  
}; 
//成员函数指针数组初始化   
State::Action Menu[] = { &State::toUp,&State::toDown,&State::toLeft,&State::toRight };  //Context
class Context{
public:Context(State *st ):st(st){ }void reset( State* st ){     this->st = st;}//转换状态void conversionState( State::Direction d ){(st->*Menu[d])(*this);}void print  (){st->print(); }~Context(){ delete st; }
private:State* st;
};//具体状态Up
class Up :public State {
public:virtual void print(){std:: cout << "now Up\n";}virtual void toDown(Context& context);
};//具体状态Down
class Down:public State {
public:virtual void print(){std:: cout << "now Down\n";}virtual void toUp(Context& context);
};//类外定义
void Up::toDown(Context& context) {context.~Context();context.reset( new Down );    
}
void Down::toUp(Context& context) {context.~Context();context.reset(new Up );    
}int main() 
{Context c(new Up);     //定义对象c.print();  //当前状态c.conversionState( State::TODOWN ); // 转换状态c.print();  //转换过的状态return 0;
}