调用派生类构造函数中的基类构造函数 [英] calling the base class constructor in the derived class constructor

问题描述

我有一个问题：

说我原来有这些类，我不能改变（让我们说他们是从一个图书馆使用）：

Say I have originally these classes which I can't change (let's say cause they're taken from a library which I'm using):

class Animal_
{
public:
    Animal_();
    int getIdA()
    {
        return idA;
    };
    string getNameA()
    {
        return nameA;
    }
private:
    string nameA;
    int idA;
}

class Farm
{
public :
    Farm()
    {
        sizeF=0;
    }
    Animal_* getAnimal_(int i)
    {
        return animals_[i];
    }
    void addAnimal_(Animal_* newAnimal)
    {
        animals_[sizeF]=newAnimal;
        sizeF++;
    }

private:
    int sizeF;
    Animal_* animals_[max];
}

但是我需要一个类，我只需要添加几个字段，这个：

But then I needed a class where I just add couple of fields so I did this:

class PetStore : public Farm
{
public :
    PetStore()
    {
     idF=0;
    };
private:
    int idF;
    string nameF;
}

但我不能初始化我的派生类，我的意思是我做了继承所以我可以添加动物到我的PetStore，但现在，因为sizeF是私人的，我该怎么做呢？我想在PetStore的默认构造函数中，我可以调用Farm（）...所以任何想法？

But I can't initialize my derived class, I mean I did this Inheritance so I can add animals to my PetStore but now since sizeF is private how can I do that? I'm thinking maybe in the PetStore default constructor I can call Farm()... so any idea?

推荐答案

PetStore 将调用 Farm 的构造函数;有
没有办法，你可以防止它。如果你什么都不做（像你做的），它将
调用默认构造函数（ Farm（））;如果你需要传递参数，
你必须在初始化器列表中指定基类：

The constructor of PetStore will call a constructor of Farm; there's no way you can prevent it. If you do nothing (as you've done), it will call the default constructor (Farm()); if you need to pass arguments, you'll have to specify the base class in the initializer list:

PetStore::PetStore()
    : Farm( neededArgument )
    , idF( 0 )
{
}

（类似地， PetStore 的构造函数将调用
nameF 。类的构造函数总是调用
的所有基类及其所有成员的构造函数。）

(Similarly, the constructor of PetStore will call the constructor of nameF. The constructor of a class always calls the constructors of all of its base classes and all of its members.)

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