Question

I have a vector of pointers to objects that are derived from the same base class. The problem is that the type of the original object is forgotten when calling functions (but not methods).

class Cat{
    //base class
public:
    virtual void growl() = 0;
};

class HouseCat : public Cat{
    //derived class
public:
    void growl(){};
};

class AlleyCat : public Cat{
    //derived class
public:
    void growl(){};
};

void function(HouseCat& a){};
void function(AlleyCat& a){};

int main(){
    vector<Cat*> cats;
    cats.push_back(new HouseCat);
    cats.push_back(new AlleyCat);
    function(*(cats[0])); //error: cannot convert parameter 1 from 'Cat' to 'HouseCat &'
    (cats[0])->growl(); //this works though

}

Is there a workaround?

Answer 1

• Add another virtual function to Cat as (add virtual destructor as well):

  class Cat{
     //base class
      ~virtual Cat() {}  //add a virtual destructor as well
       virtual void growl() = 0;
       virtual void call_function() = 0;    
  };
  

  And implement it as:

  class HouseCat : public Cat{
     //derived class
     virtual void growl(){};
     virtual void call_function() {  function(*this); }
  };
  

  Then you can write this:

  cats[0]->call_function();
  

  It will call the appropriate overload of function() eventually.

• Or simply implement function as virtual member-function in the class hierarchy.