从C++中的两个类继承的类

Question

假设我有一个类 Alcohol，它有两个派生类：Wine 和 Beer。如果我将创建一个继承自 Wine 和 Beer 的类 Cider 会发生什么？

Cider类中会出现多少份Alcohol？

我知道它可以通过虚拟继承和没有它来完成，但会有什么区别？

Answer 1

非虚拟继承：

struct Beer : Alcohol {};
struct Wine : Alcohol {};           // I'll have what he's having!

Alcohol   Alcohol                   // ...whe-ere'sh my... bayshe clashhh... hic
   ^         ^
   |         |
 Beer       Wine
    ^       ^
     \     /
      \   /
      Cider

虚拟继承：

struct Beer : virtual Alcohol {};   // virtual = doesn't get you drunk
struct Wine : virtual Alcohol {};

     Alcohol                        // you can see clearly now
     ^     ^
    /       \
 Beer       Wine
    ^       ^
     \     /
      \   /
      Cider

在非虚拟情况下，有两个不同的基础子对象。让我们开始吧：

Cider x;
Alcohol & a1 = static_cast<Beer&>(x);
Alcohol & a2 = static_cast<Wine&>(x);

assert(std::addressof(a1) != std::addressof(a2));