策略模式

            　策略模式定義了一系列的算法，並將每個算法封裝起來，並且使它們還能夠相互替換。策略模式讓算法獨立於使用它的客戶而獨立變化。
            策略模式在應用時，是根據不一樣的使用狀況動態的選擇使用的算法，對於客戶來講，提供了很好的可擴展性和封閉性。
             
                  下面是代碼示例：
                  

#ifndef STRATEGY_H

#define STRATEGY_H

#include <iostream>

class Strategy//策略基類

{

public:

 Strategy();

 virtual ~Strategy(){std::cout << "~~\n";}

 virtual void fun() = 0;

};

#endif // STRATEGY_H 
#include "strategy.h"
Strategy::Strategy()
{
}
#ifndef STRATEGYA_H
#define STRATEGYA_H
#include "strategy.h"
class StrategyA : public Strategy
{
public:
    StrategyA();
    ~StrategyA(){}
    void fun();
};
#endif // STRATEGYA_H
#include "strategya.h"
StrategyA::StrategyA()
{
}
void StrategyA::fun()
{
    std::cout << "策略A！走爲上" <<'\n';
}
#ifndef STRATEGYB_H
#define STRATEGYB_H
#include "strategy.h"
class StrategyB : public Strategy
{
public:
    StrategyB();
    ~StrategyB(){}
    void fun();
};
#endif // STRATEGYB_H
#include "strategyb.h"
StrategyB::StrategyB()
{
}
void StrategyB::fun()
{
    std::cout << "策略B！老婆天下第一，逛街去" <<'\n';
}
#ifndef STRATEGYC_H
#define STRATEGYC_H
#include "strategy.h"
class StrategyC : public Strategy
{
public:
    StrategyC();
    ~StrategyC(){}
    void fun();
};
#endif // STRATEGYC_H
#include "strategyc.h"
StrategyC::StrategyC()
{
}
void StrategyC::fun()
{
    std::cout << "策略C！金蟬脫殼" <<'\n';
}
#ifndef CONTEXT_H
#define CONTEXT_H
#include "strategy.h"
class Context//應用的上下文類
{
public:
    Context();
    Context(Strategy *p);
    ~Context(){delete p_stratery;}
    void setStratery(Strategy *p) {delete p_stratery;p_stratery = p;}
    void useStratery() const {if(p_stratery != 0)p_stratery->fun();}
private:
    Strategy *p_stratery;
};
#endif // CONTEXT_H
#include "context.h"
Context::Context():p_stratery(0)
{
}
Context::Context(Strategy *p):p_stratery(p)
{
}
#include <iostream>
using namespace std;
#include "context.h"
#include "strategya.h"
#include "strategyb.h"
#include "strategyc.h"
int main()
{
    cout << "老班讓加班！策略A..." << '\n';
    Context me(new StrategyA);
    me.useStratery();
    cout << "老婆讓逛街！策略B..." << '\n';
    me.setStratery(new StrategyB);
    me.useStratery();
    cout << "兄弟叫喝酒！可老婆讓早點回家！策略C..." << '\n';
    me.setStratery(new StrategyC);
    me.useStratery();
    return 0;
}
最後來張運行圖