派生类中的基本构造函数调用 [英] Base Constructor Call in Derived Class

问题描述

我在大学的家庭作业中遇到以下问题，任务如下：

I have got the following problem in a homework for university, the task is as follows:

派生班级 MyThickHorizo​​ntalLine 来自 MyLine 。一个要求是派生类 MyThickHorizo​​ntalLine 的构造函数本身不设置值，而是必须调用基础构造函数。

Derive a class MyThickHorizontalLine from MyLine. One requirement is that the constructor of the derived class MyThickHorizontalLine does not set the values itself, instead its obligated to call the base constructor.

目前在我的cpp文件中看起来像这样：

Which currently looks like this in my cpp file:

MyThickHorizontalLine::MyThickHorizontalLine(int a, int b, int c)
{
    MyLine(a, b, c, b);
}

这是我的Base构造函数：

This is my Base constructor:

MyLine::MyLine(int x1, int y1, int x2, int y2)
{
    set(x1, y1, x2, y2);
}

MyLine的标题定义：

Header Definition of MyLine:

public:
    MyLine(int = 0, int = 0, int = 0, int = 0);

目前的问题是，当我调试这个时，我会进入 MyThickHorizo​​ntalLine的构造函数 的价值 b c 例如 1 2 3 它们被设置那时，当我进一步进入Base构造函数时，我的所有值都为零。

Current problem is that when I debug this I step into the constructor of MyThickHorizontalLine my values for a b c are for example 1 2 3 they are set there and when I then step further and it gets into the Base constructor all my values are Zero.

我可能在这里遗漏了关于继承的关键部分，但我可以'让我明白。

I am probably missing a crucial part about inheritance here, but I can't get my mind on it.

推荐答案

MyThickHorizontalLine::MyThickHorizontalLine(int a, int b, int c)
{
     MyLine(a, b, c, b); // <<<< That's wrong
}

你无法初始化你的基类在构造函数体内。只需使用成员初始化列表来调用基类构造函数：

You cannot initialize your base class inside the constructor's body. Simply use the member initializer list to call the base class constructor:

MyThickHorizontalLine::MyThickHorizontalLine(int a, int b, int c) : MyLine(a, b, c, b) {}

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