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

 1 // test5.cpp: 定义控制台应用程序的入口点。
 2 //
 3 
 4 #include "stdafx.h"
 5 #include <iostream>
 6 
 7 class Vehicle {
 8 public:
 9     virtual double weight()const = 0;
10     virtual void start() = 0;
11     virtual Vehicle* copy() = 0;
12     virtual ~Vehicle() {};
13 };
14 
15 class RoadVehicle:public Vehicle{
16 public:
17     virtual double weight() const{
18         return 1;
19     }
20     virtual void start() {}
21     virtual Vehicle* copy() {
22         return new RoadVehicle(*this);
23     }
24     virtual ~RoadVehicle() {}
25 };
26 class AutoVehicle:public RoadVehicle{
27 public:
28     virtual double weight() const{
29         return 2;
30     }
31     virtual void start() {}
32     virtual Vehicle* copy() {
33         return new AutoVehicle(*this);
34     }
35     virtual ~AutoVehicle() {}
36 
37 };
38 
39 
40 class VehicelSurrogate {
41 public:
42     VehicelSurrogate() :vp(0) {};
43     VehicelSurrogate( Vehicle& v) :vp(v.copy()) {};
44     VehicelSurrogate(const VehicelSurrogate& v):vp(v.vp ? v.vp->copy() : 0) {};
45     ~VehicelSurrogate() {
46         delete vp;
47     };
48     VehicelSurrogate& operator=(const VehicelSurrogate& v) {
49         if (this != &v) {
50             delete vp;
51             vp = (v.vp ? v.vp->copy() : 0);
52         }
53         return *this;
54     };
55     double weight() {
56         return vp->weight();
57     }
58 
59 private:
60     Vehicle* vp;
61 };
62 
63 
64 int main()
65 {
66     VehicelSurrogate parking_lot[100];
67     AutoVehicle x;
68     parking_lot[0] = x;
69     std::cout << parking_lot[0].weight() << std::endl;;
70     return 0;
71 }