Calling the base class constructor from the derived class constructor

Question

I have a question  Say I have originally these classes which I can t change  let s say because 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      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     However  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

User · Answer

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    so I m thinking maybe in the PetStore default   constructor I can call Farm      so any Idea       Don t panic   Farm constructor will be called in the constructor of PetStore  automatically   See the base class inheritance calling rules  What are the rules for calling the superclass constructor

User · Answer

The base-class constructor is already automatically called by your derived-class constructor  In C    if the base class has a default constructor  takes no arguments  can be auto-generated by the compiler    and the derived-class constructor does not invoke another base-class constructor in its initialisation list  the default constructor will be called  I e  your code is equivalent to   class PetStore  public Farm   public       PetStore         Farm           lt ---- Call base-class constructor in initialision list            idF 0         private      int idF      string nameF

User · Answer

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          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

User · Answer

First off  a PetStore is not a farm    Let s get past this though  You actually don t need access to the private members  you have everything you need in the public interface   Animal   getAnimal  int i   void addAnimal  Animal   newAnimal     These are the methods you re given access to and these are the ones you should use      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      Simple  you call addAnimal  It s public and it also increments sizeF   Also  note that  PetStore      idF 0       is equivalent to   PetStore     Farm      idF 0       i e  the base constructor is called  base members are initialized

[c++] Calling the base class constructor from the derived class constructor

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