虚拟继承 [英] virtual inheritance

问题描述

virtual继承的意义是什么？

我看到下面的代码，不明白关键字 virtual 在以下上下文中：

  class A {}; 
 B类：public virtual A; 
  

解决方案

虚拟继承用于解决DDD问题查看下面的示例，其中有两个类继承自同一个基类：

  class Base 
 {
 
 public：
 
 virtual void Ambig 
 
}; 
  

---

  C：public Base 
 {
 
 public：
 
 // ... 
 
}; 
 
 class D：public Base 
 {
 public：
 
 // ... 
 
} 
  

---

现在，您要创建一个新类继承了C和D类（它们都继承了Base :: Ambig（）函数）：

  class Wrong：public C，public D 
 {
 
 public：
 
 ... 
 
}; 
 

在上面定义Wrong类时，实际上创建了DDD（Diamond Derivation问题）因为你不能调用：

 错误; 
 wrong.Ambig（）; 
  

这是一个模糊的函数，因为它定义了两次：

  Wrong :: C :: Base :: Ambig（）
  


$ b b

和：

  Wrong :: D :: Base :: Ambig（）
  

为了防止这种问题，你应该使用虚拟继承，这将知道引用正确的 Ambion（） function。

所以 - define：

< class C：public virtual Base

class D：public virtual Base

class Right：public C，public D


What is the meaning of "virtual" inheritance?

I saw the following code, and didn't understand the meaning of the keyword virtual in the following context:

class A {};
class B : public virtual A;

解决方案

Virtual inheritance is used to solve the DDD problem (Dreadful Diamond on Derivation).

Look at the following example, where you have two classes that inherit from the same base class:

class Base
{

public:

 virtual void  Ambig();

};

---

class C : public Base
{

public:

//...

};

class D : public Base
{
public:

    //...

};

---

Now, you want to create a new class that inherits both from C and D classes (which both have inherited the Base::Ambig() function):

class Wrong : public C, public D
{

public:

...

};

While you define the "Wrong" class above, you actually created the DDD (Diamond Derivation problem), because you can't call:

Wrong wrong;
wrong.Ambig(); 

This is an ambiguous function because it's defined twice:

Wrong::C::Base::Ambig()

And:

Wrong::D::Base::Ambig()

In order to prevent this kind of problem, you should use the virtual inheritance, which will know to refer to the right Ambig() function.

So - define:

class C : public virtual Base

class D : public virtual Base

class Right : public C, public D

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