迭代器模式[通俗易懂]

#include "stdafx.h"
#include <iostream>
#include <vector>
using namespace std;

template<typename T >
class Iterator
{
public:
        virtual ~Iterator(){};
        virtual void First() = 0;
        virtual void Next() = 0;
        virtual bool IsDone() const = 0;
        virtual  T* CurrentItem() = 0;
};

template<typename T >
class ConcreteAggregate ;

template<typename T >
class Aggregate
{
public:
        virtual ~Aggregate() {};
        virtual Iterator< T>* CreateIterator() = 0;
};

template<typename T >
class ConcreteIterator :public Iterator <T >
{
private:
        ConcreteAggregate<T >* m_pAggre;
        int current = 0;
public:
        virtual ~ConcreteIterator()
       {
               delete m_pAggre;
       }
       ConcreteIterator( ConcreteAggregate<T >* pAggre ) :m_pAggre(pAggre), current(0)
       {}

        virtual void First()
       {
              current = 0;
       }

        virtual void Next()
       {
               if (current < m_pAggre->GetLen())
                     ++current;
       }

        virtual bool IsDone() const
       {
               return (current >= m_pAggre->GetLen());
       }

        virtual T* CurrentItem()
       {
               if (current <= m_pAggre->GetLen())
                      return &(*m_pAggre)[current];
               else
                      return NULL;
       }

};

template<typename T >
class ConcreteAggregate :public Aggregate <T >
{
private:
        vector< T> m_Data;
public:
       ConcreteAggregate()
       {
              m_Data.push_back(1);
              m_Data.push_back(2);
              m_Data.push_back(3);
       }

        virtual Iterator< T>* CreateIterator()
       {
               return new ConcreteIterator<T >(this );
       }

        T& operator[]( int index)
       {
               return m_Data[ index];
       }

        int GetLen()
       {
               return m_Data.size();
       }
};

// IteratorPattern.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "Iterator.h"
#include <iostream>

int _tmain (int argc , _TCHAR * argv [])
{
        Aggregate< int>* pAgg = new ConcreteAggregate<int >();
        Iterator< int>* it = pAgg->CreateIterator();
        for (it->First(); !it->IsDone(); it->Next())
       {
              std::cout <<*( it->CurrentItem() )<< std::endl;
       }

       getchar();
        return 0;
}