迭代器模式，提供一种方法顺序访问一个聚合对象中各个元素，而不暴露该对象的内部表示。该模式很好理解，C++中的迭代器应该都用过，和那个差不多。其UML图如下： ConcreteIterator内部有一个聚合对象的引用（指针），而ConcreteAggregate依赖于ConcreteIterator。以前向链表为例，示例代码如下：
// IteratorModel.h文件 #pragma once #include <iostream> // 单向链表 template<typename T> class node { public: node() : next(nullptr) { } T data; node * next; }; // 迭代器 template<typename T> class IteratorBase { public: virtual T first() = 0; virtual T next() = 0; virtual bool isDone() = 0; virtual T currentItem() = 0; }; template<typename T> class Iterator; // 单项链表 template<typename T> class forwardlist { public: forwardlist(); ~forwardlist(); private: unsigned int m_nLength; node<T> * m_HeadNode; public: friend class Iterator<T>; T getElement(unsigned int index); T getFirst(); T getTail(); unsigned int insertElement(unsigned int index, T elem); unsigned int appendElement(T elem); unsigned int insertFirst(T elem); unsigned int setValue(unsigned int index, T value); T deleteElement(unsigned int index); void deleteAll(); unsigned int getLength(); bool empty(); Iterator<T> createIterator(); private: node<T> * getFirstNode(); node<T> * getNode(unsigned int index); }; // 具体的迭代器 template<typename T> class Iterator : public IteratorBase<T> { private: forwardlist<T> * m_list; node<T> * m_pCurrentNode; unsigned int m_nCurrentIndex; public: Iterator(forwardlist<T> * p):m_pCurrentNode(nullptr), m_nCurrentIndex(0u) { m_list = p; m_pCurrentNode = m_list->getFirstNode(); } T first() { return m_list->getFirst(); } T next() { if (isDone()) return 0; if (nullptr == m_pCurrentNode) m_pCurrentNode = m_list->getNode(m_nCurrentIndex); node<T> * p = m_pCurrentNode->next; m_pCurrentNode = p; m_nCurrentIndex++; return p->data; } T currentItem() { return m_pCurrentNode->data; } bool isDone() { if (m_nCurrentIndex< m_list->getLength()) return false; return true; } T operator*() { return currentItem(); } }; // forwardlist函数实现 // 创建迭代器函数 template<typename T> Iterator<T> forwardlist<T>::createIterator() { return Iterator<T>(this); } template<typename T> forwardlist<T>::forwardlist() : m_nLength(0u), m_HeadNode(nullptr) { m_HeadNode = new node<T>; } template<typename T> forwardlist<T>::~forwardlist() { deleteAll(); delete m_HeadNode; } template<typename T> node<T> * forwardlist<T>::getNode(unsigned int index) { if (index >= m_nLength) { std::cout << "out of ranges" << std::endl; return 0; } unsigned int n = 0; node<T> * pnode = m_HeadNode; while (n++ <= index) { pnode = pnode->next; } return pnode; } template<typename T> T forwardlist<T>::getElement(unsigned int index) { return getNode(index)->data; } template<typename T> T forwardlist<T>::getFirst() { return getElement(0u); } template<typename T> T forwardlist<T>::getTail() { if (m_nLength == 0u) { return T; } return getElement(m_nLength - 1); } template<typename T> unsigned int forwardlist<T>::insertElement(unsigned int index, T elem) { if (index > m_nLength) { std::cout << "out of ranges" << std::endl; return 0; } node<T> * pnode = m_HeadNode; unsigned int n = 0u; while (n++ < index)// 定位到index上一个节点 { pnode = pnode->next; } // 插入节点 node<T> *pnodeElem = new node<T>; pnodeElem->data = elem; pnodeElem->next = pnode->next; pnode->next = pnodeElem; // 长度增加 m_nLength++; return index; } template<typename T> unsigned int forwardlist<T>::insertFirst(T elem) { return insertElement(0u, elem); } template<typename T> unsigned int forwardlist<T>::appendElement(T elem) { return insertElement(m_nLength, elem); } template<typename T> unsigned int setValue(unsigned int index, T value) { if (index >= m_nLength) { std::cout << "out of ranges" << std::endl; return 0; } node<T> * pnode = m_HeadNode; while (n++ <= index)// 定位到index { pnode = pnode->next; } pnode->data = value; return index; } template<typename T> T forwardlist<T>::deleteElement(unsigned int index) { if (index >= m_nLength) { std::cout << "out of ranges" << std::endl; return 0; } unsigned int n = 0u; node<T> * pnode = m_HeadNode; while (n++ < index)// 定位到index上一个节点 { pnode = pnode->next; } // 删除节点 node<T> * pnodeTemp = pnode->next; pnode->next = pnodeTemp->next; T tTemp = pnodeTemp->data; delete pnodeTemp; pnodeTemp = nullptr; // 长度减一 m_nLength--; return tTemp; } template<typename T> void forwardlist<T>::deleteAll() { while (m_nLength > 0) { deleteElement(0); } m_HeadNode->next = nullptr; } template<typename T> unsigned int forwardlist<T>::getLength() { return m_nLength; } template<typename T> bool forwardlist<T>::empty() { return m_nLength > 0 ? false : true; } template<typename T> node<T> * forwardlist<T>::getFirstNode() { return getNode(0u); }测试代码如下：
#include <iostream> #include "IteratorModel.h" int main() { using namespace std; // 迭代器模式 forwardlist<char> list; list.insertElement(0u, 'A'); list.insertElement(1u, 'B'); list.insertElement(2u, 'C'); Iterator<char> it = list.createIterator(); std::cout << *it << endl; std::cout << it.next() << endl; std::cout << it.next() << endl; cout << it.first() << endl; cout << *it << endl; if (!it.isDone()) cout << "结束" << endl; else cout << "未结束" << endl; getchar(); return 0; }测试结果如下图：
