前景提要C++中，内部类可以访问外部内的私有变量和函数，只不过需要先引入外部类的对象。

class A{
private:
    int a;
    int b;
    class InnerA{
        int inner_a;
        int inner_b;
        InnerA(A* objA){
            inner_a = objA->a;
            inner_b = objA->b;
        }
    };
};

迭代器：提供一种方法顺序访问一个聚合对象中各个元素, 而又无须暴露该对象的内部表示。

Iterator.h

#ifndef ITERATOR_H_
#define ITERATOR_H_
#include<iostream>
using namespace std;
/**
 * 迭代器抽象接口
 * 
*/
class Iterator{
public:
    virtual bool hasNext() = 0;
    virtual int next() = 0;
    virtual ~Iterator(){}
};
#endif

Container.h

#ifndef CONTAINER_H_
#define CONTAINER_H_
#include<iostream>
using namespace std;
#include<vector>
#include "Iterator.h"

/**
 * 容器抽象类
*/
class Container{
public:
    virtual Iterator* getIterator() = 0;
    virtual ~Container(){}
};
#endif

MyCon.h

class MyCon : public Container{
private:
    int* start;
    int* tail;
    int* end;
public:
    MyCon(){
        start = new int[100];
        tail = start;
    }
    // 获取迭代器
    Iterator* getIterator(){
        return new MyIterator(this);
    }
    // 添加元素
    void push_back(int& value){
        *tail = value;
        tail++;
    }

    ~MyCon(){
        delete[] start;
    }
protected:
    class MyIterator : public Iterator{
        public:
            int* inner_start;
            int* inner_tail;
            MyIterator(MyCon* mycon){
                inner_start = mycon->start;
                inner_tail = mycon->tail;
            }
            virtual bool hasNext(){
                if(inner_start < inner_tail){
                    return true;
                }
                return false;
            }
            virtual int next(){
                int cur = *inner_start;
                inner_start++;
                return cur;
            }
    };
};

main.cpp

#include<iostream>
using namespace std;
#include "Container.h"

int main(){
    MyCon mycon;
    int a = 1;
    mycon.push_back(a);
    a = 2;
    mycon.push_back(a);
    a = 3;
    mycon.push_back(a);
    Iterator* itr = mycon.getIterator();
    while(itr->hasNext()){
        cout << itr->next() << endl;
    }
    return 0;
}

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