在C++中使用虚基类的目的是可以在使用间接共同基类时只保留一份成员。因为一个基类可以在生成一个派生类时作为虚基类，当生成另一个类时可以不作为虚基类，这样就保证了派生类中只保留一份基类的成员。
#include
using namespace std;
class animal
{
public:
animal(int ia)
{
a=ia;
cout<<"in animal constructor"<<endl;
}
~animal()
{
cout<<"in animal deconstructor"<<endl;
}
void breath()
{
cout<<"can breath:"<<a<<endl;
}
private:
int a;
};
class bird:virtual public animal
{
public:
bird(int ia):animal(ia)
{
cout<<"in bird constructor"<<endl;
}
~bird()
{
cout<<"in bird deconstructor"<<endl;
}
void fly()
{
cout<<"in bird deconstructor"<<endl;
}
};
class fish:virtual public animal
{
public:
fish(int ia):animal(ia)
{
cout<<"in fish constructor"<<endl;
}
~fish()
{
cout<<"in fish deconstructor"<<endl;
}
};
class flyfish:public bird,public fish
{
public:
flyfish(int ia):animal(ia),bird(ia),fish(ia)
{
cout<<"in flyfish constructor"<<endl;
}
~flyfish()
{
cout<<"in flyfish deconstructor"<<endl;
}
void fly()
{
cout<<"flyfish is flying"<<endl;
}
};
void main()
{
flyfish ff(10);
ff.fly();
ff.breath();
}