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?

Answer 1

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.)