[C++]迭代器模式

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种元素，而又不暴露该对象的内部表示。

 // 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//// 参考大话设计模式#include <iostream>
#include <vector>using namespace std;class Iterator {
public:virtual string First() = 0;virtual string Next() = 0;virtual bool IsEnd() = 0;virtual string GetCurrent() = 0;
};class Aggregate {
public:virtual void Push(const string& str) = 0;virtual string Pop(int index) = 0;virtual size_t Count() = 0;virtual Iterator* CreateIterator() = 0;
};class ConcreteIterator : public Iterator {
public:ConcreteIterator(Aggregate* aggregate) {aggregate_ = aggregate;}string First() {return aggregate_->Pop(0);}string Next() {if (current_ + 1 < aggregate_->Count()) {current_++;return aggregate_->Pop(current_);}else {return "";}}bool IsEnd() {if (current_ + 1 == aggregate_->Count()) {return true;}else {return false;}}string GetCurrent() {return aggregate_->Pop(current_);}private:Aggregate* aggregate_ = nullptr;size_t current_ = 0;
};class ConcreteAggregate : public Aggregate {
public:ConcreteAggregate() {}~ConcreteAggregate () {if (iterator_ != nullptr) {delete iterator_;iterator_ = nullptr;}}void Push(const string& str) {vec_str_.push_back(str);}string Pop(int index) {return vec_str_[index];}size_t Count() {return vec_str_.size();}Iterator* CreateIterator() {if (iterator_ == nullptr) {iterator_ = new ConcreteIterator(this);}return iterator_;}private:vector<string> vec_str_;Iterator* iterator_ = nullptr;
};int main()
{ConcreteAggregate* concrete_aggregate = new ConcreteAggregate();concrete_aggregate->Push("a");concrete_aggregate->Push("b");concrete_aggregate->Push("c");concrete_aggregate->Push("d");Iterator* iterator = concrete_aggregate->CreateIterator();;cout << iterator->First() << endl;while (!iterator->IsEnd()) {cout << iterator->Next() << endl;}return 0;
}