STL中的集合都有Iterator，Iterator模式的作用是遍历集合中的元素．它的实现原理为遍历封装在一个类中进行（Iterator类），这样避免了暴露这个聚合对象内部．
Iterator模式如下图：
实现： //Aggregate.h
#ifndef AGGREGATE_H_ #define AGGREGATE_H_ typedef int Object; class Iterator; class Aggregate { public: Aggregate(){} virtual ~Aggregate(){} virtual Iterator* CreateIterator()=0; virtual Object GetItem(int idx)=0; virtual int GetSize()=0; protected: }; class ConcreteAggregate:public Aggregate { public: //enum{SIZE=3}; static const int SIZE=3; ConcreteAggregate(); ~ConcreteAggregate(); Iterator* CreateIterator(); Object GetItem(int idx); int GetSize(); private: Object objs_[SIZE]; }; #endif //AGGREGATE_H_//Aggregate.cpp
#include"Aggregate.h" #include "Iterator.h" #include <iostream> ConcreteAggregate::ConcreteAggregate() { for (int i = 0; i < SIZE; ++i) objs_[i] = i; } ConcreteAggregate::~ConcreteAggregate() {} Iterator* ConcreteAggregate::CreateIterator() { return new ConcreteIterator(this, 0); } Object ConcreteAggregate::GetItem(int idx) { if (idx < GetSize()) return objs_[idx]; else return -1; } int ConcreteAggregate::GetSize() { return SIZE; }//Iterator.h
#ifndef ITERATOR_H_ #define ITERATOR_H_ class Aggregate; typedef int Object; class Iterator { public: virtual ~Iterator(); virtual void First()=0; virtual void Next()=0; virtual bool IsDone() = 0; virtual Object CurrentItem() = 0; protected: Iterator(); }; class ConcreteIterator :public Iterator { public: ConcreteIterator(Aggregate* ag, int idx = 0); ~ConcreteIterator(); void First(); void Next(); bool IsDone(); Object CurrentItem(); private: Aggregate* ag_; int idx_; }; #endif//Iterator.cpp
#include"Aggregate.h" #include "Iterator.h" #include <iostream> Iterator::Iterator() {} Iterator::~Iterator() {} ConcreteIterator::ConcreteIterator(Aggregate* ag, int idx) { ag_ = ag; idx_ = idx; } ConcreteIterator::~ConcreteIterator() {} Object ConcreteIterator::CurrentItem() { return ag_->GetItem(idx_); } void ConcreteIterator::First() { idx_ = 0; } void ConcreteIterator::Next() { if (idx_ < ag_->GetSize()) ++idx_; } bool ConcreteIterator::IsDone() { return idx_ == ag_->GetSize(); }//main.cpp
#include "Aggregate.h" #include "Iterator.h" #include <iostream> int main() { Aggregate* ag = new ConcreteAggregate(); for (Iterator* it = new ConcreteIterator(ag); !it->IsDone(); it->Next()) { std::cout << it->CurrentItem() << std::endl; } return 0; }