C++设计模式学习笔记三：策略模式

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1、先看看策略模式的官方定义：

The Strategy Pattern defines a family of algorithms,encapsulates each one,and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.（策略模式定义了一系列的算法，并将每一个算法封装起来，而且使它们还可以相互替换。策略模式让算法独立于使用它的客户而独立变化。）

策略模式类图如下：

2、《大话设计模式》实现策略模式中，使用到了反射。前面也说过，在C++中实际没有反射，需要自己实现。为实现反射，我模仿MFC中RTTI的dynamic调用，利用链表实现了个简单的反射功能。代码如下：

ReflectionFunc.h

#pragma once#include "stdafx.h"#include <string>#include <map>#include <vector>using namespace std;typedef void* (*CreateFunc)();struct ClassFactory{std::string m_strName;CreateFunc m_pObject;static void* GetClassByName(std::string strName);static ClassFactory* pFirstClass;ClassFactory* m_pNextClass;};struct MY_CLASSINIT{ MY_CLASSINIT(ClassFactory* pNewClass); };#define DECLARE_MYCLASS(class_name) \static void* CreateObject(class_name);\static ClassFactory m_CF##class_name;#define IMPLEMENT_MYCLASS(class_name)\static char my##class_name[] = #class_name;\void* class_name::CreateObject(class_name) { return new class_name; }\ClassFactory class_name::m_CF##class_name = {my##class_name, (CreateFunc)class_name::CreateObject};\static MY_CLASSINIT _init_##class_name(&class_name::m_CF##class_name);

ReflectionFunc.cpp

#pragma once#include "StdAfx.h"#include "ReflectionFunc.h"ClassFactory* ClassFactory::pFirstClass = NULL;void* ClassFactory::GetClassByName(std::string strName){void* pObject=NULL;ClassFactory* pClass = pFirstClass;for (;pClass!=NULL;pClass=pClass->m_pNextClass){if (pClass->m_strName.compare(strName) == 0){pObject = pClass->m_pObject();}}return pObject;}MY_CLASSINIT::MY_CLASSINIT(ClassFactory* pNewClass){pNewClass->m_pNextClass = ClassFactory::pFirstClass;ClassFactory::pFirstClass = pNewClass;}

3、策略模式的其他部分代码实现如下：

CashContext.h

#pragma once#include "StrategyPattern.h"#include "CashSuper.h"#include <string>using namespace std;class STRATEGYPATTERN_API CCashContext{public:CCashContext(void);~CCashContext(void);void SetBehavior(std::string strClassName, char szParam[]);double GetResult(double money);private:CCashSuper* m_pCashSuper;};

CashContext.cpp

#pragma once#include "StdAfx.h"#include "CashContext.h"#include "ReflectionFunc.h"CCashContext::CCashContext(void){}CCashContext::~CCashContext(void){}void CCashContext::SetBehavior(std::string strClassName, char szParam[]){CCashSuper* pCash = (CCashSuper*)ClassFactory::GetClassByName(strClassName);if (!pCash) return;pCash->SetClassParam(szParam);m_pCashSuper = pCash;}double CCashContext::GetResult(double money){return m_pCashSuper->acceptCash(money);}

CashSuper.h

#pragma once#include <vector>#include "ReflectionFunc.h"class CCashSuper{public:CCashSuper(void);~CCashSuper(void);virtual void SetClassParam(const char* pParam)=0;virtual double acceptCash(double money)=0;};

CashRebate.h

#pragma once#include "cashsuper.h"#include "Utility.h"class CCashRebate :public CCashSuper{public:DECLARE_MYCLASS(CCashRebate)CCashRebate(void);~CCashRebate(void);virtual void SetClassParam(const char* pParam);virtual double acceptCash(double money);private:double m_Rebate;};

CashRebate.cpp

#pragma once#include "StdAfx.h"#include "CashRebate.h"IMPLEMENT_MYCLASS(CCashRebate)CCashRebate::CCashRebate(void){m_Rebate = 1;}CCashRebate::~CCashRebate(void){}double CCashRebate::acceptCash(double money){return money * m_Rebate;}void CCashRebate::SetClassParam(const char* pParam){std::string str(pParam);std::vector<string> vecStr;CUtility::GetInstance().SplitString(str, vecStr);m_Rebate = atof(vecStr[0].c_str());}

其他策略方法CCashReturn、CCashNormal类实现与CCashRebate类似，这里就不copy出来了。

完整的代码下载地址如下：

http://download.csdn.net/detail/cz168love/7573781

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