策略模式與狀態(tài)模式看起來差不多，只是從概念上側(cè)重不同。策略模式封裝的是策略或算法，狀態(tài)模式封裝的是狀態(tài)，主要區(qū)別在于封裝對象的不同形式。

以下代碼定義了兩種算法策略類。

#include <iostream>

using namespace std;

class Strategy
{
public:
    virtual ~Strategy(){}
    virtual void AlgorithmInterface() = 0;
};

class ConcreteStrategyA:public Strategy
{
public:
    void AlgorithmInterface()
    {
        cout<<__PRETTY_FUNCTION__<<endl;
    }
};
class ConcreteStrategyB:public Strategy
{
public:
    void AlgorithmInterface()
    {
        cout<<__PRETTY_FUNCTION__<<endl;
    }
};

以下代碼實現(xiàn)了策略的使用者類。

class Context
{
private:
    Strategy* m_pStrategy;
public:
    Context(Strategy* strategy):m_pStrategy(strategy){}
    void SetStrategy(Strategy* strategy)
    {
        m_pStrategy = strategy;
    }
    void ContextInterface()
    {
        m_pStrategy->AlgorithmInterface();
    }
};

以下代碼演示了策略模式，通過對context對象切換策略，切換了其同一接口的算法實現(xiàn)。

int main(void){
    Strategy* strategyA = new ConcreteStrategyA();
    Strategy* strategyB = new ConcreteStrategyB();
    Context context(strategyA);
    context.ContextInterface();
    context.SetStrategy(strategyB);
    context.ContextInterface();
    delete strategyA;
    delete strategyB;
    return 0;
}

輸出

virtual void ConcreteStrategyA::AlgorithmInterface()
virtual void ConcreteStrategyB::AlgorithmInterface()