c++沉思录 学习笔记 第五章 代理类

Vehicle 一个车辆的虚基类

class Vehicle {
public:
virtual double weight()const = 0;
virtual void start() = 0;
virtual Vehicle* copy() = 0;
virtual ~Vehicle() {};
};

衍生出RoadVehicle AutoVehicle两个类

如果有一个停车场类 可以容纳100辆车

一开始计划 有Vehicle[100]这种变量来表示停车场

但是Vehicle是虚基类 不能有实例化的实体 也就不会有数组

所以需要一个代理类来保存Vehicle的指针 它可以指向任意的Vehicle的衍生类

同时考虑到拷贝操作 添加了拷贝函数

class VehicelSurrogate {
public:
VehicelSurrogate() :vp(0) {};
VehicelSurrogate( Vehicle& v) :vp(v.copy()) {};
VehicelSurrogate(const VehicelSurrogate& v):vp(v.vp ? v.vp->copy() : 0) {};
~VehicelSurrogate() {
delete vp;
};
VehicelSurrogate& operator=(const VehicelSurrogate& v) {
if (this != &v) {
delete vp;
vp = (v.vp ? v.vp->copy() : 0);
}
return *this;
};
double weight() {
return vp->weight();
}

private:
Vehicle* vp;
};

如此 就可以使用VehicelSurrogate[100]来表示停车场的概念

完整代码如下

// test5.cpp: 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>

class Vehicle {
public:
    virtual double weight()const = 0;
    virtual void start() = 0;
    virtual Vehicle* copy() = 0;
    virtual ~Vehicle() {};
};

class RoadVehicle:public Vehicle{
public:
    virtual double weight() const{
        return 1;
    }
    virtual void start() {}
    virtual Vehicle* copy() {
        return new RoadVehicle(*this);
    }
    virtual ~RoadVehicle() {}
};
class AutoVehicle:public RoadVehicle{
public:
    virtual double weight() const{
        return 2;
    }
    virtual void start() {}
    virtual Vehicle* copy() {
        return new AutoVehicle(*this);
    }
    virtual ~AutoVehicle() {}

};


class VehicelSurrogate {
public:
    VehicelSurrogate() :vp(0) {};
    VehicelSurrogate( Vehicle& v) :vp(v.copy()) {};
    VehicelSurrogate(const VehicelSurrogate& v):vp(v.vp ? v.vp->copy() : 0) {};
    ~VehicelSurrogate() {
        delete vp;
    };
    VehicelSurrogate& operator=(const VehicelSurrogate& v) {
        if (this != &v) {
            delete vp;
            vp = (v.vp ? v.vp->copy() : 0);
        }
        return *this;
    };
    double weight() {
        return vp->weight();
    }

private:
    Vehicle* vp;
};


int main()
{
    VehicelSurrogate parking_lot[100];
    AutoVehicle x;
    parking_lot[0] = x;
    std::cout << parking_lot[0].weight() << std::endl;;
    return 0;
}