迭代器模式（Iterator）：提供一种方法顺序访问一个聚合对象中的各个元素，而又不暴露该对象的内部表示。
使用场景：当我们需要访问一个聚集对象时，而且不管这些对象是什么都需要遍历的时候，我们可以考虑使用迭代器模式。如果我们需要对聚集有多种方式遍历时，也可以考虑使用迭代器模式。迭代器一般需要提供开始，下一个，，是否结束，当前项的内容等方法。
#ifndef ITERATOR_H#define ITERATOR_H#include<iostream>#include<string>#include<deque>using namespace std;class Aggregate{friend class Iterator;public:Aggregate(){}virtual Iterator *CreateIterator()=0;};class ConcreteAggregate :public Aggregate{friend class ConcreteIterator;deque<string> passengers;public:Iterator * CreateIterator();int Count();void Add(string st);string This(int index);};void ConcreteAggregate::Add(string st){passengers.push_back(st);}string ConcreteAggregate::This(int index){return passengers.at(index);}int ConcreteAggregate::Count(){return passengers.size();}class Iterator{public:Iterator(){}virtual string First() = 0;virtual string Next() = 0;virtual bool IsDone() = 0;virtual string CurrentItem() = 0;};class ConcreteIterator :public Iterator{friend class ConcreteAggregate;ConcreteAggregate aggregate;int current = 0;public:ConcreteIterator(ConcreteAggregate );string First();string Next();bool IsDone();string CurrentItem();};ConcreteIterator::ConcreteIterator(ConcreteAggregate ar) :aggregate(ar), current(ar.passengers.size()-1){}std::string ConcreteIterator::First(){return aggregate.This(0);}std::string ConcreteIterator::Next(){string temp;–current;if (current>=0)temp = aggregate.This(current);return temp;}bool ConcreteIterator::IsDone(){return current >=0 ? false : true;}std::string ConcreteIterator::CurrentItem(){return aggregate.This(current);}Iterator * ConcreteAggregate::CreateIterator(){return (new ConcreteIterator(*this));}#endif#include"Iterator.h"int main(){ConcreteAggregate pa;pa.Add("大鸟");pa.Add("小菜");pa.Add("行李");pa.Add("老外");pa.Add("公交内部员工");pa.Add("小偷");ConcreteIterator Itr(pa);string temp = Itr.First();while (!Itr.IsDone()){cout << Itr.CurrentItem() << " 请买票。\n";Itr.Next();}return 0;}
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