iterator(迭代器模式)

引入

在想显示数组当中所有元素时，我们往往会使用下面的for循环语句来遍历数组

#include <iostream>
#include <vector>int main()
{std::vector<int> v({ 1, 2, 3 });for (int i = 0; i < v.size(); i++){std::cout << v[i] << " " << std::endl;}return 0;
}

下面我们来对比一下，下面这一段遍历代码

#include <iostream>
#include <map>int main()
{std::map<int, int> mp;mp[0] = 1;mp[1] = 2;mp[2] = 3;for(std::map<int, int>::iterator iter = mp.begin(); iter != mp.end(); iter ++){std::cout << "key is " << iter->first << " " << "value is " << iter->second << std::endl;}return 0;
}

二者在功能上实际上是一样的，都是对数据进行遍历输出。
在第一段代码当中，变量i的作用是为了在自增之后，用做访问下一个元素的下标。
在第二段代码当中,变量*iter*也是在自增之后，用来访问mp的下一个元素，我们可以发现, 实际上在第二段代码当中，iterator是对i的一个抽象化、通用化的表达，这就是我们要学习的iterator模式。

iterator模式主要作用是对数据集合按照顺序进行遍历，在遍历的同时还要保证内部信息的封装性,只提供遍历接口。
iterator模式常用于stl容器当中,比如map,list等

UML类图

iterator类图

具体代码

book.h

#ifndef __BOOK_H__
#define __BOOK_H__#include <iostream>
#include <string>class Book
{
public:Book(std::string name):m_nameStr(name){std::cout << "value";};~Book() = default;Book(const Book &other) = default;Book& operator=(const Book &other) = default;Book& operator=(Book &&other) = delete;std::string getName() const{return m_nameStr;};
protected:private:std::string m_nameStr;
};#endif //__BOOK_H__

bookshelf.h

#ifndef __BOOKSHELF_H__
#define __BOOKSHELF_H__#include <vector>
#include "book.h"class BookShelf
{
public:BookShelf() = default;~BookShelf() = default;BookShelf(const BookShelf &other) = default;BookShelf& operator=(const BookShelf &other) = default;BookShelf(BookShelf &&other) = delete;BookShelf& operator=(BookShelf &&other) = delete;//实现iteratorclass iterator{public:iterator(Book* tmp = nullptr) :iteratorPtr(tmp) {};iterator& operator++(){iteratorPtr++;return *this;};bool operator==(const iterator& other) const{return this->iteratorPtr == other.iteratorPtr;}bool operator!=(const iterator& other) const{return !(*this == other);}Book& operator*(){return *iteratorPtr;}private:Book* iteratorPtr = nullptr;};//提供遍历起点iterator begin();//提供遍历终点iterator end();//添加书籍void addBook(const Book& tmpBook);
protected:private:std::vector<Book> m_bookList;
};#endif //__BOOKSHELF_H__

bookshelf.cpp

#include "bookshelf.h"BookShelf::iterator BookShelf::begin()
{return iterator(&m_bookList[0]);
}BookShelf::iterator BookShelf::end()
{return iterator(&(m_bookList.back()));
}void BookShelf::addBook(const Book& tmpBook)
{m_bookList.emplace_back(tmpBook);
}

main.cpp

#include "book.h"
#include "bookshelf.h"int main()
{Book book1("第一本书");Book book2("第二本书");Book book3("第三本书");BookShelf woodBookShelf;woodBookShelf.addBook(book1);woodBookShelf.addBook(book2);woodBookShelf.addBook(book3);//得不到vector最后一个元素的后一个地址,所以只会输出//第一本书、第二本书for(BookShelf::iterator iter = woodBookShelf.begin(); iter != woodBookShelf.end(); ++iter){std::cout << (*iter).getName() << std::endl;}system("pause");return 0;
}