虚基类/虚继承

菱形继承是多重继承中跑不掉的，Java拿掉了多重继承，辅之以接口。C++中虽然没有明确说明接口这种东西，但是只有纯虚函数的类可以看作Java中的接口。在多重继承中建议使用“接口”，来避免多重继承中可能出现的各种问题。

示例代码：

#include <iostream>
using namespace std;
class Vehicle
{
public:
    int MaxSpeed;
    int Weight;
    void Run() {cout << "vehicle run!" << endl;}
    void Stop() {cout << "vehicle stop!" << endl;}
//    virtual void Run() {cout << "vehicle run!" << endl;}
//    virtual void Stop() {cout << "vehicle stop!" << endl;}
};
class Bicycle : virtual public Vehicle
{
public:
    int Height;
    void Run() {cout << "bicycle run!" << endl;}
    void Stop() {cout << "bicycle stop!" << endl;}
};
class Motorcar : virtual public Vehicle
{
public:
    int SeatNum;
    void Run() {cout << "motocar run!" << endl;}
    void Stop() {cout << "motocar stop!" << endl;}
};
class Motorcycle : public Bicycle, public Motorcar
{
public:
    void Run() {cout << "motocycle run!" << endl;}
    void Stop() {cout << "motocycle stop!" << endl;}
};
int main()
{
    Vehicle v;
    v.Run();
    v.Stop();
    Bicycle b;
    b.Run();
    b.Stop();
    Motorcar m;
    m.Run();
    m.Stop();
    Motorcycle mc;
    mc.Run();
    mc.Stop();
    Vehicle* vp = &v;
    vp->Run();
    vp->Stop();
    vp = &b;
    vp->Run();
    vp->Stop();
    vp = &m;
    vp->Run();
    vp->Stop();
    vp = &mc;
    vp->Run();
    vp->Stop();
    return 0;
}