从子类的构造函数体调用基类的构造函数 [英] Calling a constructor of the base class from a subclass' constructor body

问题描述

我的印象是，这是不可能的，例如：


但是下面的程序运行并产生两行Constructor Person：

I was under impression that it's impossible, see for example: Calling the constructor of the base class after some other instructions in C++
But the following program runs and produces two lines of "Constructor Person":

#include <iostream>

class Person
{
public:
    Person() 
    { 
        std::cout << "Constructor Person" << std::endl; }
    };

class Child : public Person
{
public:
    Child() 
    { 
        c = 1; 
        Person(); 
    }
    int c;
};

int main() 
{
    Child child;
    return 0;
}

第一个是隐式调用默认构造函数，很清楚。第二个 - 这是否意味着标题中描述的行动是合法的？我使用Visual C ++ 2010。

The first one is implicit call of the default constructor, that's clear. What about the 2nd one - does it mean that the action described in the title is legitimate? I use Visual C++ 2010.

推荐答案

以下是加速C ++的摘录：
派生对象构造方式：

1.为整个对象（基类成员以及派生类成员）分配空间;

2.调用基类构造函数来初始化base-对象的类部分;

3.按构造函数初始化程序的指示初始化派生类的成员;

4.执行派生类构造函数的主体（如果有） 。

The following is an excerpt from "Accelerated C++": "Derived objects are constructed by:
1. Allocating space for the entire object (base class members as well as derived class members);
2. Calling the base-class constructor to initialize the base-class part of the object;
3. Initializing the members of the derived class as directed by the constructor initializer;
4. Executing the body of the derived-class constructor, if any."

总结回答和注释：从子类的构造函数体中调用基类的构造函数是不可能的，因为＃2必须在＃4之前。
但是我们仍然可以在派生构造函数体中创建一个基础对象，从而调用一个基础构造函数。它将是一个与使用当前执行的派生构造函数构造的对象不同的对象。

Summarizing the answers and comments: Calling a constructor of the base class from a subclass' constructor body is impossible in the sense that #2 above must precede #4. But we still can create a base object in the derived constructor body thus calling a base constructor. It will be an object different from the object being constructed with the currently executed derived constructor.

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