[C++_8]繼承_2

13.4 多重繼承與虛繼承(is-a)

虛擬繼承是多重繼承中特有的概念。虛擬基類是爲解決多重繼承而出現的。如:類D繼承自類B1、B2，而類B1、B2都繼承自類A，因此在類D中兩次出現類A中的變量和函數。爲了節省內存空間，可以將B1、B2對A的繼承定義爲虛擬繼承，而A就成了虛擬基類。實現的代碼如下：

class A
class B1:public virtual A;
class B2:public virtual A;

class D:public B1,public B2;

#include<iostream>
#include<string>
using namespace std;

class Goods
{

  double m_price;
  int  m_weight;
public:
  Goods(double price,int weight):m_price(price),m_weight(weight){cout<< "Goods構造"<< endl;};
  ~Goods(){cout << "Goods析構"<<endl;};
  void show(){cout << "價格是:" << m_price <<endl << "重量是:"<< m_weight<< endl;}
  double getprice(){return m_price;};
};

class Camera : virtual public Goods //虛繼承
{
protected:
  string m_type;
public:
  Camera(double price,int weight,string type):Goods(price,weight),m_type(type)
  {
	cout << "Camera構造！" << endl;
  };
  ~Camera()
  {
	cout << "Camera析構！" << endl;
  };  
  
  void take(const char *obj)
  {
	cout << "給" << obj << "照相"<< endl;
  };
};

class Mp3: virtual public Goods       //虛繼承
{
  string m_band;
public:
  Mp3(double price, int weight,string band):Goods(price,weight),m_band(band)
  {
	cout << "Mp3構造！" << endl;
  };
  ~Mp3()
  {
	cout << "Mp3析構！" << endl;
  };
  void play(const char* songname)
  {
	cout << "正在播放" << songname<<endl;
  };
};

class SmartPhone: public Camera,public Mp3//多重繼承&虛繼承 is-a 
{
public:
  SmartPhone(double price , int weight,string type,string band)
  :Goods(price, weight),Camera(price ,weight,type),Mp3(price,weight,band)
  {
	cout << "SmatrPhone構造！" << endl;
  };
  ~SmartPhone()
  {
	cout << "SmartPhone析構！" << endl;
  };
  void call(const char* who)
  {
	cout << "給"<<who<<"打電話！" <<endl;
  };
};


int main()
{
  SmartPhone sp(200,2,"單反","蘋果");
  sp.show();
  sp.take("tiger");
  sp.call("家裏");
  return 0;
}

輸出結果：

13.5 多重繼承變成組合方式（has-a）

class MordenPhone    //組合方式 has-a
{
  Goods g;
  Camera c;
  Mp3 m;
public:
  MordenPhone(double price,int weight,string type,string band)
  :g(price ,weight),c(price,weight,type),m(price,weight,band)
  {
	cout << "MordenPhone構造！" << endl;
  };
  ~MordenPhone()
  {
	cout << "MordenPhone析構！" << endl;
	
  };
  double getprice()
  {
	return m.getprice();
  };
};

int main()
{
  MordenPhone mp(2000,3,"數碼","三星");
  cout << "MordenPhone's price is" << mp.getprice() << endl;
}