多继承从基类转换到不同的派生类 [英] Multiple inheritance casting from base class to different derived class

问题描述

让我们假设有这样的类层次结构：

Let's assume there is such class hierarchy:

class A //base class

class B //interface

class C : public A, public B

创建C对象：

A *object = new C();

是否可以将对象传递给B？

Is it possible to cast object to B ?

重要：我假设我不知道对象是C.我只知道它实现了接口B

Important: I assume I don't know that object is C. I just know that it implements interface B

推荐答案

否。这是不可能的（直接从 A * 到 B * ）。

No. This is not possible (direct casting from A* to B*).

因为 A 和 B 的地址位于类C 。因此，投射会始终不安全，并且可能会出现意外行为。 演示。

Because the address of A and B are at different locations in class C. So the cast will be always unsafe and possibly you might land up in unexpected behavior. Demo.

投射应始终通过 class C 。例如

A* pa = new C();
B* pb = static_cast<C*>(pa);
                   ^^^^ go through class C

Demo

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