策略模式

#include <iostream>
#include <string>

using namespace std;

class Stratergy {

public:
    virtual void AlgoInterface() = 0;  //注意，基类的虚函数需要有实现，否则会出现Link2001错误；也可以定义为纯虚函数来解决.
};

class ConcreteStragergyA : public Stratergy {

public:
    void AlgoInterface();

};

class ConcreteStragergyB : public Stratergy {

public:
    void AlgoInterface();

};

class ConcreteStragergyC : public Stratergy {

public:
    void AlgoInterface();

};

class Context {
public:
    Context(): m_st(NULL) {}
    Context(string type);
    ~Context();

    void getRlt();

private:
    Stratergy *m_st;
};

void ConcreteStragergyA::AlgoInterface() {
    cout<<"This is A algo"<<endl;
}

void ConcreteStragergyB::AlgoInterface() {
    cout<<"This is B algo"<<endl;
}

void ConcreteStragergyC::AlgoInterface() {
    cout<<"This is C algo"<<endl;
}

Context::Context(string type) {
    if (type == "A") {
        m_st = new ConcreteStragergyA();
    } else if (type == "B") {
        m_st = new ConcreteStragergyB();
    } else {
        m_st = new ConcreteStragergyC();
    }
}

Context::~Context() {
    if (m_st) {
        delete m_st;
    }
}

void Context::getRlt() {
    if (m_st) {
        m_st->AlgoInterface();
    }
}

void main() {

    {
        Context A("A");
        A.getRlt();
        Context B("B");
        B.getRlt();
        Context C("C");
        C.getRlt();
    }

    system("pause");
}

注解：

1. 更加抽象低耦合，使用中用户只需使用Context类，不必关注每个strategy的实现。