#include <iostream>
//基類
using namespace std;
class CBase
{
protected:
int a;
public:
CBase(int na)
{
a=na;
cout<<"CBase constructor! "<<endl;
}
~CBase(){cout<<"CBase deconstructor! "<<endl;}
};
//派生類1(聲明CBase爲虛基類)
class CDerive1:virtual public CBase
{
public:
CDerive1(int na):CBase(na)
{
cout<<"CDerive1 constructor! "<<endl;
}
~CDerive1(){cout<<"CDerive1 deconstructor! "<<endl;}
int GetA(){return a;}
};
//派生類2(聲明CBase爲虛基類)
class CDerive2:virtual public CBase
{
public:
CDerive2(int na):CBase(na)
{
cout<<"CDerive2 constructor! "<<endl;
}
~CDerive2(){cout<<"CDerive2 deconstructor! "<<endl;}
int GetA(){return a;}
};
//子派生類
class CDerive12:public CDerive1,public CDerive2
{
public:
CDerive12(int na1,int na2,int na3):CDerive1(na1),CDerive2(na2),CBase(na3)
{
cout<<"CDerive12 constructor! "<<endl;
}
~CDerive12(){cout<<"CDerive12 deconstructor! "<<endl;}
};
int main()
{
CDerive12 obj(100,200,300);
//得到從CDerive1繼承的值
cout<<" from CDerive1 : a = "<<obj.CDerive1::GetA();
//得到從CDerive2繼承的值
cout<<" from CDerive2 : a = "<<obj.CDerive2::GetA()<<endl<<endl;
return 0;
}
參考: http://blog.chinaunix.net/uid-26983585-id-3309645.html
http://blog.csdn.net/livelylittlefish/article/details/2171267
http://blog.sina.com.cn/s/blog_4a286b4e010125rk.html
c++ 引入虛基類的原因是多繼承產生了二義性。
虛基類的構造函數先於非虛基類的構造函數執行
在類中,如果什麼都沒有,則類佔用1個字節,一旦類中有其他的佔用空間成員,則這1個字節就不在計算之內,如一個類只有一個int則佔用4字節而不是5字節。如果只有成員函數,則還是隻佔用1個字節,因爲類函數不佔用空間。
虛函數因爲存在一個虛函數表,需要4個字節,數據成員對象如果爲指針則爲4字節,注意有字節對齊,如果爲13字節,則進位到16字節空間。