c++迭代器模式

1.迭代器模式简介

   迭代器模式提供了一种方法顺序访问一个聚合对象中的各个元素，而又无需暴露该对象的内部实现，这样既可以做到不暴露集合的内部结构，又可让外部代码透明地访问集合内部的数据。

2.源码实现

#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:
    Aggregate(){};
    virtual ~Aggregate(){};
    virtual int Count() = 0;
    virtual void Push(const string &strValue) = 0;
    virtual string Pop(const int index) = 0;
    virtual Iterator *CreateIterator() = 0;
};

class ConcreteIterator : public Iterator
{
public:
    ConcreteIterator(Aggregate *pAggregate) : Iterator()
    {
        m_nCurrent = 0;
        m_Aggregate = pAggregate;
    }

    string First()
    {
        return m_Aggregate->Pop(0);
    }

    string Next()
    {
        string strRet;
        m_nCurrent++;

        if(m_nCurrent < m_Aggregate->Count())
        {
            strRet = m_Aggregate->Pop(m_nCurrent);
        }

        return strRet;
    }

    string GetCur()
    {
        return m_Aggregate->Pop(m_nCurrent);
    }

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

private:
    int m_nCurrent;
    Aggregate *m_Aggregate;
};

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

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

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

        return m_pIterator;
    }

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

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

    string Pop(const int index)
    {
        string strRet;

        if(index < Count())
        {
            strRet = m_vecItems[index];
        }

        return strRet;
    }

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

int main(int argc, char **argv)
{
    ConcreteAggregate *pName = new ConcreteAggregate();
    if(pName == NULL)
        return -1;

    pName->Push("hello");
    pName->Push("world");
    pName->Push("cxue");

    Iterator *iter = NULL;
    iter = pName->CreateIterator();

    if(iter != NULL)
    {
        string strItem = iter->First();

        while(!iter->IsEnd())
        {
            cout << iter->GetCur() << " is ok" << endl;
            iter->Next();
        }
    }   

    delete pName;

    return 0;
}

3.编译源码

$ g++ -o example example.cpp

4.运行及其结果

$ ./example
hello is ok
world is ok
cxue is ok