迭代器模式

前言

迭代器模式就是分离了集合对象的遍历行为，抽象出一个迭代器类来负责，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。
迭代器模式在访问数组、集合、列表等数据时，尤其是数据库数据操作时，是非常普遍的应用，但由于它太普遍了，所以各种高级语言都对它进行了封装，所以反而给人感觉此模式本身不太常用了。
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代码

Aggregate.h

#ifndef AGGREGATE_H
#define AGGREGATE_H#include <string>
#include "Iterator.h"using namespace std;class Aggregate {
public:virtual ~Aggregate() = default;virtual int count() = 0;virtual void push(const string &strValue) = 0;virtual string pop(int idx) = 0;virtual Iterator *createIterator() = 0;
};
#endif //AGGREGATE_H

ConcreteAggregate.h

#ifndef CONCRETEAGGREGATE_H
#define CONCRETEAGGREGATE_H#include <vector>
#include "Aggregate.h"
#include "ConcreteIterator.h"class ConcreteAggregate : public Aggregate {
public:ConcreteAggregate();~ConcreteAggregate() override;Iterator *createIterator() override;int count() override;void push(const string &strValue) override;string pop(int idx) override;
private:vector <string> m_vecItems;Iterator *m_pIterator;
};#endif //CONCRETEAGGREGATE_H

ConcreteAggregate.cpp

#include "ConcreteAggregate.h"ConcreteAggregate::ConcreteAggregate() : m_pIterator(nullptr) {m_vecItems.clear();
}ConcreteAggregate::~ConcreteAggregate() {if (m_pIterator != nullptr) {delete m_pIterator;m_pIterator = nullptr;}
}int ConcreteAggregate::count() {return m_vecItems.size();
}void ConcreteAggregate::push(const string &strValue) {m_vecItems.push_back(strValue);
}string ConcreteAggregate::pop(int idx) {string strRet;if (idx < count()) {strRet = m_vecItems[idx];}return strRet;
}Iterator *ConcreteAggregate::createIterator() {if(m_pIterator == nullptr){m_pIterator = new ConcreteIterator(this);}return m_pIterator;
}

Iterator.h

#ifndef ITERATOR_H
#define ITERATOR_H#include <string>using namespace std;class Iterator {
public:Iterator() = default;virtual ~Iterator() = default;virtual string first() = 0;virtual string next() = 0;virtual string getCurr() = 0;virtual bool isEnd() = 0;
};
#endif //ITERATOR_H

ConcreteIterator.h

#ifndef CONCRETEITERATOR_H
#define CONCRETEITERATOR_H#include "Iterator.h"
#include "Aggregate.h"class ConcreteIterator : public Iterator {
public:explicit ConcreteIterator(Aggregate *pAggregate);string first() override;string next() override;string getCurr() override;bool isEnd() override;
private:Aggregate *m_Aggregate;int m_nCurrent;
};#endif //CONCRETEITERATOR_H

ConcreteIterator.cpp

#include "ConcreteIterator.h"ConcreteIterator::ConcreteIterator(Aggregate *pAggregate) : m_nCurrent(0), Iterator() {m_Aggregate = pAggregate;
}string ConcreteIterator::first() {return m_Aggregate->pop(0);
}string ConcreteIterator::next() {string strRet;m_nCurrent++;if (m_nCurrent < m_Aggregate->count()) {strRet = m_Aggregate->pop(m_nCurrent);}return strRet;
}string ConcreteIterator::getCurr() {return m_Aggregate->pop(m_nCurrent);
}bool ConcreteIterator::isEnd() {return (m_nCurrent >= m_Aggregate->count());
}

main.cpp

#include <iostream>
#include "iterator.h"
#include "ConcreteAggregate.h"using namespace std;int main() {auto *pName = new ConcreteAggregate();pName->push("hello");pName->push("word");pName->push("cue");Iterator *iter = pName->createIterator();if (iter != nullptr) {string strItem = iter->first();while (!iter->isEnd()) {cout << iter->getCurr() << " is ok" << endl;iter->next();}}return 0;
}