一个继承自c ++中两个类的类

Question

假设我有一个 Alcohol 类，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 Cider 类会怎么样？

Cider 课程中会出现多少 Alcohol 副本？

我知道可以使用虚拟继承来完成它，但没有它，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));