迭代器模式用于解決順序訪問聚合對(duì)象問題。C++的容器與迭代器就是典型的實(shí)現(xiàn)。

以下代碼定義了一個(gè)單向鏈表節(jié)點(diǎn)。

#include <iostream>

using namespace std;

class Node
{
public:
    Node(int val):value(val),Next(nullptr){}
    class Node* Next;
    int value;
};

以下代碼定義了迭代器以及它的基本迭代功能。

class Iterator
{
public:
    virtual ~Iterator(){}
    virtual void First() = 0;
    virtual void Next() = 0;
    virtual Node* Current() = 0;
};

class NodeIterator:public Iterator
{
private:
    Node* CurrentPtr;
    class NodeContainer* nodeContainer;
public:
    NodeIterator(class NodeContainer* container):nodeContainer(container),CurrentPtr(nullptr){}
    void First();
    void Next()
    {
        if (CurrentPtr)
        {
            CurrentPtr = CurrentPtr->Next;
        }
    }
    Node* Current()
    {
        return CurrentPtr;
    }
};

以下代碼定義了容器以及它的基本修改功能。

class Container
{
public:
    virtual ~Container(){}
    virtual Iterator* CreateIterator() = 0;
};

class NodeContainer:public Container
{
public:
    Node *Begin, *End;
    NodeContainer():Begin(nullptr),End(nullptr){}
    Iterator* CreateIterator()
    {
        return new NodeIterator(this);
    }
    void AddEnd(Node* node)
    {
        if (End != nullptr)
        {
            End->Next = node;
        }
        node->Next = nullptr;
        End = node;
        if (Begin == nullptr)
        {
            Begin = node;
        }
    }
    void RemoveBegin()
    {
        if (Begin != nullptr)
        {
            Node* Current = Begin;
            Begin = Begin->Next;
            delete Current;
        }
    }
};

void NodeIterator::First()
{
    CurrentPtr = nodeContainer->Begin;
}

以下代碼演示了迭代器模式。首先創(chuàng)建容器，對(duì)容器內(nèi)容進(jìn)行修改，然后創(chuàng)建迭代器，進(jìn)行迭代訪問。

int main(void){
    NodeContainer container;
    for (int i = 0; i < 5; ++i)
    {
        Node* node = new Node(i);
        container.AddEnd(node);
    }
    for (int i = 0; i < 2; ++i)
    {
        container.RemoveBegin();
    }
    NodeIterator* pIt = dynamic_cast<NodeIterator*>(container.CreateIterator());
    pIt->First();
    if (pIt->Current() != nullptr)
    {
        cout<<"Begin->"<<pIt->Current()->value;
        pIt->Next();
    }
    for (; pIt->Current(); pIt->Next())
    {
        cout<<"->"<<pIt->Current()->value;
    }
    cout<<"->End"<<endl;
    return 0;
}

輸出

Begin->2->3->4->End