Question

I am trying to implement a Singleton class in C++ and getting a bit confused. Ok, let’s say I have the following 2 classes:

class Animal {

public:
    virtual int age() = 0;
    virtual void breed() = 0;   
};


class Cat : public Animal {
  public:
Cat();
int age();
void breed();  
};                

more classes involved in this system …. (dog, fish etc)

Now I have a singleton class which I can just use 1 object:

class Singleton 
{
  public:
    Animal *newAnimal(string theTypeOfAnimal);
  private:   
   static Animal* pinstance;
};                        

Animal *Singleton::newAnimal(string theTypeOfAnimal)
{
pinstance = new Cat;

}           

int main()
{        
Singleton *s;
return 0;
}      

UPDATE:

New code:

#include <iostream>
using namespace std;

class Animal {

public:
    virtual int age() = 0;
    virtual void breed() = 0;
};

class Cat : public Animal
{
public:
        virtual int age() { return 9; }
        virtual void breed() { }

 };
class Singleton
{
public:
    Animal *newAnimal(string theTypeOfAnimal);
  private:   
   static Animal* pinstance;
};

Animal* Singleton::pinstance = 0;


Animal *Singleton::newAnimal(string theTypeOfAnimal)
{
     this->pinstance = new Cat;
 return pinstance;
}  

 int main(int argc, char *argv[]) {

Singleton s;

Animal *myAnimal = NULL;

Animal *myAnimal = s->newAnimal("cat");

}

Answer 1

You must define static class object outside of it:

Animal* Singleton::pinstance = 0;

You must define functions in Cat class:

class Cat : public Animal
{
public:
    Cat() {}
    int age() { return 7; }
    void breed() {}
};