继承层次结构：构造函数&析构函数执行顺序 [英] Inheritance hierarchy: Constructor & Destructor execution sequence

问题描述

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

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

要执行的第一个构造函数是层次结构中任何地方的虚拟基类。

我尝试使用以下程序进行验证：

I tried to verify it using following program:

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

每个班级都有一个c'tor和虚拟d'tor。输出如下：

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 . . .

但根据报价，虚拟基类的构造函数应首先执行。

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

我理解错了什么？

编辑：为了澄清我的问题，根据我的理解，这种行为没有任何作用与基类是否为虚拟有关。但引用坚持使用 Virtual Base class 。我清楚了吗？还是有什么东西可疑？

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?

推荐答案

如果不首先构建继承自它们的类，则无法构造虚拟基类。因此，在您的情况下，将构造非虚拟基类，因为虚拟基类依赖于它们： C 直到 A 和 B 。因此， A 和 B 实际上是在 C 之前构造的，即使 C 实际上是继承的。

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.

这篇关于继承层次结构：构造函数&析构函数执行顺序的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！