Lists and Iterators c++ are the topics bothering me these days a lot

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Hallo
I am new to c++ and learning this Lists and Iterators from quite a few days.
I am stuck and confused now.
First what I got to know abouts Lists and Iterators were
Lists ist just like a normal list in which you can push your objects or values(strings, int and so on) like we do in stack
Iterators are just to poitn out the stuff we pushed in and we can also know what we pushed up just by dereferecing it.
Now my question is Why some people put a pointer with a datatype sometimes. For eg
std::list<animals*> animal_list; // where animal is my class
std::list<animals*> ::iterator iter; //
We do this to access the pointers to the class animals for eg I tried making this code

C++

#include <stdio.h>
#include <iostream>
#include <list>
#include <string>
using namespace std;
class Animals
{
public:
	void getName(){
		cout << "this is a"<< *it;
	}
};
class Dog : public Animals{
public:
	Dog(string dog){
		cout << "the breed of the dog is"<< dog<< endl ;
	}
};
class Cat : public Animals{
public:
	Cat(string colour){
		cout << "the color of the cst is"<<colour<<endl;
	}
};
class Rabbit : public Animals{
public:
	Rabbit(string colour){
		cout << "the color of the rabbit is"<< colour<<endl;
	}
};
int main()
{
	list<animals*> animals;
	Dog *d = new Dog("labrador");
	Cat *c = new Cat("braun");
	Rabbit *r = new Rabbit("black n white");
	animals.push_back(d);
	animals.push_back(c);
	animals.push_back(r);
	list<animals*>::iterator it;
	for (it = animals.begin(); it != animals.end(); ++it){
		cout << (*it)->getName(); // here I'm gettng error because of << operands. 
	}	
}

In this case I made 3 derived classes and all these are inheriting animals class. My main purpose is to access the function getName() declared in base class.
Now I made three pointers pointing to these classes. And then I pushed them up in the list in order to have the dog, cat and rabbit in my list. I don't know if I'm right or wrong.
I am really screwed up.Its not getting in my head.
Please help and sorry for such a lng description. I just wanted to clearly explain myself
Thanks
P.s : Please don't get confuse after reading it.

Posted 15-Jul-15 22:51pm

Member 11841297

Updated 15-Jul-15 23:46pm

Frankie-C

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Richard MacCutchan · Answer 1 · 2015-07-16T00:35:00

Solution 1

You are calling getName() on your Animals pointer, but that function calls some iterator that is not defined in the class. You should change your classes to something like:

C++

class Animal
{
protected string _animal;
public:
    Animal(string type)
    {
        _animal = type;
    }

};
class Dog : public Animal
{
public:
    string getName()
    {
        return _animal + " is a dog";
    }
};

Posted 16-Jul-15 0:35am

Richard MacCutchan

Comments

Member 11841297 16-Jul-15 6:47am

you are declaring getName fucntion in class dog instead of doing it in Base class. And then how would I define it in main class.?
and do I need to declare the function in a1l classes?.

Richard MacCutchan 16-Jul-15 6:59am

Yes, because each Animal returns a different string for getName() that includes the Animal type. This is just an example of how it can be done, not how it must be done. If you do not declare it in all classes then you need a version in the Animal class that provides the default answer.

You need to spend more time learning the basics about classes before worrying about Lists and iterators.

CPallini · Answer 2 · 2015-07-16T01:02:00

Possibly you mean something like:

C++

 #include <iostream>
 #include <list>
 #include <string>
 using namespace std;


class Animals
{
public:
  virtual void showName(){
    cout << "this is a animal" << endl;
  }
  virtual ~Anumals(){}
};
class Dog : public Animals{
  string breed;
public:
  Dog(string breed):breed(breed){}
  void showName()
  {
    cout << "the breed of the dog is " << breed << endl ;
  }
};
class Cat : public Animals{
string colour;
public:
  Cat(string colour):colour(colour){}
  void showName()
  {
    cout << "the colour of the cat is " << colour << endl;
  }
};
class Rabbit : public Animals{
string colour;
public:
  Rabbit(string colour):colour(colour){}
  void showName()
  {
    cout << "the colour of the rabbit is "<< colour << endl;
  }
};
int main()
{
  list<Animals*> animals;
  Dog *d = new Dog("labrador");
  Cat *c = new Cat("braun");
  Rabbit *r = new Rabbit("black n white");
  animals.push_back(d);
  animals.push_back(c);
  animals.push_back(r);
  list<Animals*>::iterator it;
  for (it = animals.begin(); it != animals.end(); ++it){
    (*it)->showName(); 
  }
  for (it = animals.begin(); it != animals.end(); ++it)
    delete (*it);
}