继承hierachy：构造函数&析构函数执行序列 [英] Inheritance hierachy: Constructor & Destructor execution sequence

问题描述

此处 http://www.parashift.com/c++-faq -lite / multiple-inheritance.html section [25.14]

要执行的第一个构造函数

我尝试使用以下程序验证它：

  A（纯虚拟）
 | 
 B 
 | 
 C 
（虚拟）/ \（虚拟）
 E D 
 \ / 
 F 
 | 
 G（纯虚拟）
 | 
 H 
  

每个类都有一个c'tor和虚拟对手。输出如下：

  A 
 B 
 C 
 E 
 D 
 F 
 G 
 H 
〜H 
〜G 
〜F 
〜D 
〜E 
 〜C 
〜B 
〜A 
按任意键继续。 。 。 
  

但是应该首先执行虚拟基类构造函数。

编辑：要清除我的问题，根据我的理解，这种行为没有什么关于基类是否是虚拟的。但是在虚拟基本类中强制引用。

感谢。

解决方案

如果不继承它们继承的类，则不能构造虚拟基类。所以在你的情况下，非虚拟基类是构造的，因为虚拟的依赖于它们： C 不能被构造，直到 A 和 B 是。因此， A 和 B 的确在 C 即使 C 实际上是继承的。

Here http://www.parashift.com/c++-faq-lite/multiple-inheritance.html section [25.14] says

The very first constructors to be executed are the virtual base classes anywhere in the hierarchy.

I tried to verify it using following program:

           A (pure virtual)
           |
           B
           |
           C
(virtual)/   \ (virtual)
       E       D
         \   /
           F
           |
           G (pure virtual)
           |
           H

each class has a c'tor and virtual d'tor. the output is as follows:

A
B
C
E
D
F
G
H
~H
~G
~F
~D
~E
~C
~B
~A
Press any key to continue . . .

but as per quote virtual base classes constructors should be executed first.

what did I undestand wrong?

EDIT: To clear my question, As per my understanding this behaviour has nothing to do with whether a base class is virtual or not. but quote insists on Virtual Base class. am i clear or something fishy there?

Thanks.

解决方案

Virtual base classes cannot be constructed if the classes they inherit from are not constructed first. So in your case, non-virtual base classes are constructed because the virtual ones depend on them: C can't be constructed until A and Bare. Therefore, A and B are indeed constructed before C, even though C is virtually inherited.

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