c++设计模式----迭代器模式iterator

迭代器：
    意图：
        提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。
    适用性：
        访问一个聚合对象的内容而无需暴露它的内部表示。

        支持对聚合对象的多种遍历。

        为遍历不同的聚合结构提供一个统一的接口(即, 支持多态迭代)。

                                  

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

class Iterator
{
public:
  Iterator(){}
  virtual ~Iterator(){};
  virtual string First() = 0;
  virtual string Next() = 0;
  virtual string GetCur() = 0;
  virtual bool IsEnd() = 0;
};

class Aggregate
{
public:
  virtual int Count() = 0;
  virtual void Push(const string &strValue) = 0;
  virtual string POp(const int cnt) = 0;
  virtual Iterator* CreateIterator() = 0;
};

class ConcreteIterator : public Iterator
{
public:
  ConcreteIterator(Aggregate *p_aggregate):m_aggregate(p_aggregate),m_cnt(0){}
  
  string First()
  {
    return m_aggregate->POp(0);
  }

  string Next()
  {
    string str;
    m_cnt++;
    if (m_cnt < m_aggregate->Count())
    {
      str = m_aggregate->POp(m_cnt);
    }

    return str;
  }

  string GetCur()
  {
    return m_aggregate->POp(m_cnt);
  }

  bool IsEnd()
  {
    return m_cnt >= m_aggregate->Count() ? true : false;
  }

  ~ConcreteIterator(){ }

private:
  Aggregate *m_aggregate;
  int m_cnt;
};

class ConcreteAggregate : public Aggregate
{
public:
  ConcreteAggregate() :m_pIterator(NULL)
  {
    m_vecItem.clear();
  }

  ~ConcreteAggregate()
  {
    if (NULL != m_pIterator)
    {
      delete m_pIterator;
      m_pIterator = NULL;
    }
  }

  int Count()
  {
    return m_vecItem.size();
  }

  void Push(const string &strValue)
  {
    m_vecItem.push_back(strValue);
  }

  string POp(const int cnt)
  {
    string str;
    if (cnt < Count())
    {
      str = m_vecItem[cnt];
    }
    return str;
  }

  Iterator* CreateIterator()
  {
    if (NULL == m_pIterator)
    {
      m_pIterator = new ConcreteIterator(this);
    }

    return m_pIterator;
  }

private:
  vector<string> m_vecItem;
  Iterator *m_pIterator;
};

int main()
{
  ConcreteAggregate* pName = NULL;
  pName = new ConcreteAggregate();
  if (NULL != pName)
  {
    pName->Push("hello");
    pName->Push("word");
    pName->Push("cxue");
  }
  Iterator* iter = NULL;
  iter = pName->CreateIterator();
  if (NULL != iter)
  {
    string strItem = iter->First();
    while (!iter->IsEnd())
    {
      cout << iter->GetCur() << " is ok" << endl;
      iter->Next();
    }
  }
  system("pause");

  return 0;
}

改进一下也许更好懂一点：

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

class Iterator
{
public:
  Iterator(){}
  virtual ~Iterator(){};
  virtual string First() = 0;
  virtual string Next() = 0;
  virtual string GetCur() = 0;
  virtual bool IsEnd() = 0;
};

class Aggregate
{
public:
  virtual int Count() = 0;
  virtual void Push(const string &strValue) = 0;
  virtual string POp(const int cnt) = 0;
};

class ConcreteIterator : public Iterator
{
public:
  ConcreteIterator(Aggregate *p_aggregate):m_aggregate(p_aggregate),m_cnt(0){}
  
  string First()
  {
    return m_aggregate->POp(0);
  }

  string Next()
  {
    string str;
    m_cnt++;
    if (m_cnt < m_aggregate->Count())
    {
      str = m_aggregate->POp(m_cnt);
    }

    return str;
  }

  string GetCur()
  {
    return m_aggregate->POp(m_cnt);
  }

  bool IsEnd()
  {
    return m_cnt >= m_aggregate->Count() ? true : false;
  }

  ~ConcreteIterator(){ }

private:
  Aggregate *m_aggregate;
  int m_cnt;
};

class ConcreteAggregate : public Aggregate
{
public:
  ConcreteAggregate()
  {
    m_vecItem.clear();
  }

  ~ConcreteAggregate()
  {
  }

  int Count()
  {
    return m_vecItem.size();
  }

  void Push(const string &strValue)
  {
    m_vecItem.push_back(strValue);
  }

  string POp(const int cnt)
  {
    string str;
    if (cnt < Count())
    {
      str = m_vecItem[cnt];
    }
    return str;
  }

private:
  vector<string> m_vecItem;
};

int main()
{
  ConcreteAggregate* pName = NULL;
  pName = new ConcreteAggregate();
  if (NULL != pName)
  {
    pName->Push("hello");
    pName->Push("word");
    pName->Push("cxue");
  }

  Iterator* iter = new ConcreteIterator(pName);

  if (NULL != iter)
  {
    string strItem = iter->First();
    while (!iter->IsEnd())
    {
      cout << iter->GetCur() << " is ok" << endl;
      iter->Next();
    }
  }

  delete iter;
  iter = NULL;

  system("pause");

  return 0;
}