一个继承自c ++中两个类的类

Question

假设我有一个酒类,它有两个派生类:葡萄酒和啤酒.如果我将制作一个继承了Wine和Beer的类Cider,会发生什么？

在Cider类中会出现多少份酒精？

我知道它可以通过虚拟继承来完成而没有它,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.让我们来看看他们:

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

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