[c++]代理对象模式

代理对象

#include <iostream>#include <vector>using namespace std;class Vehicle { public:  Vehicle() {}  virtual string getName() = 0;};class Car : public Vehicle { public:  Car() {    name = "car";  }  virtual string getName() {    return name; }  ~Car() {    cout << "delete" << endl;  }private:  string name;};class Bike : public Vehicle { public:  Bike() {}  virtual string getName() { return "bike"; }private:  string name;};void wrong_code(vector<Vehicle *> &parkinglot) {  Car c;  cout << &c << endl;  parkinglot[0] = &c;  //将c插入到parkinglot内  cout << &(*parkinglot[0]) << endl;}int main() {  vector<Vehicle *> parkinglot(1);  wrong_code(parkinglot);  cout << parkinglot[0]->getName() << endl;  // Oops!!parkinglot内存的地址指向了一块被销毁的内存  cout << &(*parkinglot[0]) << endl;  return 0;}

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在这种情况下会出现因为临时对象在生命周期结束之后，对象上的内存被释放，所以访问它的数据就会出现不可预计的结果。

在这种大前提下,代理类就顺势而生了.

顾名思义,代理类就是指某个基类以及其子类的代理,其功能是使之能在容器中也表现出多态性.而没有动态内存管理的烦恼.

现在定义Vehicle以及子类的代理类VehicleSurrogate.

#include <iostream>#include <vector>using namespace std;class Vehicle { public:  Vehicle() {}  virtual string getName() = 0;  virtual Vehicle *copy() const = 0;  virtual ~Vehicle() {}  //虚析构函数是为了支持多态.但是本例中并不需要. private:};class Car : public Vehicle { public:  Car() { name = "car"; }  virtual string getName() { return name; }  virtual Vehicle *copy() const { return new Car; }  virtual ~Car() {} private:  string name;};class Bike : public Vehicle { public:  Bike() { name = "bike"; }  virtual string getName() { return name; }  virtual Vehicle *copy() const { return new Bike; }  virtual ~Bike() {} private:  string name;};class VehicleSurrogate { public:  VehicleSurrogate() : p(0) {}  VehicleSurrogate(const Vehicle &v) : p(v.copy()) {}  VehicleSurrogate(const VehicleSurrogate &vs) : p(vs.p ? vs.p->copy() : 0) {}  VehicleSurrogate &operator=(const VehicleSurrogate &vs) {    if (this !=        &vs)  //在删除p之前一定得记得判断vs和this是不是同一个,否则会有问题    {      delete p;      p = vs.p->copy();    }    return *this;  }  string getName() { return p->getName(); }  ~VehicleSurrogate() { delete p; } private:  Vehicle *p;};void right_code(vector<VehicleSurrogate> &parkinglot) {  Car c;  parkinglot.push_back(c);}int main() {  vector<VehicleSurrogate> parkinglot;  right_code(parkinglot);  cout << parkinglot[0].getName() << endl;  return 0;}

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所以，这种代理对象的模式实际上就是对对象的封装，同时处理他们对他们进行资源管理，从而防止指针对象指向未被析构的对象地址，已经内存泄露的问题。

示例来自