list的反向迭代器
reverse.h
#pragma once
namespace mudan
{
template<class Iterator, class Ref, class Ptr>
struct __reverse_iterator
{
Iterator _cur;
typedef __reverse_iterator<Iterator, Ref, Ptr> RIterator;
__reverse_iterator(Iterator it)
:_cur(it)
{}
RIterator operator++()
{
--_cur;
return *this;
}
RIterator operator--()
{
++_cur;
return *this;
}
Ref operator*()
{
//return *_cur;
auto tmp = _cur;
--tmp;
return *tmp;
}
Ptr operator->()
{
//return _cur.operator->();
return &(operator*());
}
bool operator!=(const RIterator& it)
{
return _cur != it._cur;
}
};
}
list.h
#include<assert.h>
#include<iostream>
#include<algorithm>
#include"reverse.h"
using namespace std;
namespace mudan
{
template<class T>
struct list_node
{
T _data;
list_node<T>* _next;
list_node<T>* _prev;
list_node(const T& x = T())
:_data(x)
, _next(nullptr)
, _prev(nullptr)
{}
};
// typedef __list_iterator<T, T&, T*> iterator;
// typedef __list_iterator<T, const T&, const T*> const_iterator;
// 像指针一样的对象
template<class T, class Ref, class Ptr>
struct __list_iterator
{
typedef list_node<T> Node;
typedef __list_iterator<T, Ref, Ptr> iterator;
typedef bidirectional_iterator_tag iterator_category;
typedef T value_type;
typedef Ptr pointer;
typedef Ref reference;
typedef ptrdiff_t difference_type;
Node* _node;
__list_iterator(Node* node)
:_node(node)
{}
bool operator!=(const iterator& it) const
{
return _node != it._node;
}
bool operator==(const iterator& it) const
{
return _node == it._node;
}
// *it it.operator*()
// const T& operator*()
// T& operator*()
Ref operator*()
{
return _node->_data;
}
//T* operator->()
Ptr operator->()
{
return &(operator*());
}
// ++it
iterator& operator++()
{
_node = _node->_next;
return *this;
}
// it++
iterator operator++(int)
{
iterator tmp(*this);
_node = _node->_next;
return tmp;
}
// --it
iterator& operator--()
{
_node = _node->_prev;
return *this;
}
// it--
iterator operator--(int)
{
iterator tmp(*this);
_node = _node->_prev;
return tmp;
}
};
template<class T>
class list
{
typedef list_node<T> Node;
public:
typedef __list_iterator<T, T&, T*> iterator;
typedef __list_iterator<T, const T&, const T*> const_iterator;
typedef __reverse_iterator<iterator, T&, T*> reverse_iterator;
typedef __reverse_iterator<const_iterator, const T&, const T*> const_reverse_iterator;
const_iterator begin() const
{
return const_iterator(_head->_next);
}
const_iterator end() const
{
return const_iterator(_head);
}
iterator begin()
{
return iterator(_head->_next);
}
iterator end()
{
return iterator(_head);
}
reverse_iterator rbegin()
{
return reverse_iterator(end());
}
reverse_iterator rend()
{
return reverse_iterator(begin());
}
void empty_init()
{
// 创建并初始化哨兵位头结点
_head = new Node;
_head->_next = _head;
_head->_prev = _head;
}
template <class InputIterator>
list(InputIterator first, InputIterator last)
{
empty_init();
while (first != last)
{
push_back(*first);
++first;
}
}
list()
{
empty_init();
}
void swap(list<T>& x)
//void swap(list& x)
{
std::swap(_head, x._head);
}
// lt2(lt1)
list(const list<T>& lt)
{
empty_init();
list<T> tmp(lt.begin(), lt.end());
swap(tmp);
}
// lt1 = lt3
list<T>& operator=(list<T> lt)
{
swap(lt);
return *this;
}
~list()
{
clear();
delete _head;
_head = nullptr;
}
void clear()
{
iterator it = begin();
while (it != end())
{
it = erase(it);
}
}
void push_back(const T& x)
{
//Node* tail = _head->_prev;
//Node* newnode = new Node(x);
_head tail newnode
//tail->_next = newnode;
//newnode->_prev = tail;
//newnode->_next = _head;
//_head->_prev = newnode;
insert(end(), x);
}
void push_front(const T& x)
{
insert(begin(), x);
}
iterator insert(iterator pos, const T& x)
{
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* newnode = new Node(x);
// prev newnode cur
prev->_next = newnode;
newnode->_prev = prev;
newnode->_next = cur;
cur->_prev = newnode;
return iterator(newnode);
}
void pop_back()
{
erase(--end());
}
void pop_front()
{
erase(begin());
}
iterator erase(iterator pos)
{
assert(pos != end());
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* next = cur->_next;
prev->_next = next;
next->_prev = prev;
delete cur;
return iterator(next);
}
private:
Node* _head;
};
void test()
{
list<int> ls;
ls.push_back(1);
ls.push_back(2);
ls.push_back(3);
ls.push_back(4);
ls.push_back(5);
ls.push_back(6);
for (auto& e : ls)
{
cout << e << " ";
}
cout << endl;
list<int>copy = ls;
for (auto e : copy)
{
cout << e << " ";
}
}
}
test.cpp
#include"list.h"
#include<list>
int main(void)
{
mudan::test();
//list<int>ls;
//ls.push_back(1);
//ls.push_back(2);
//ls.push_back(3);
//ls.push_back(4);
//ls.push_back(5);
//ls.push_back(6);
//for (auto e : ls)
//{
// cout << e << " ";
//}
//cout << endl;
//list<int>lt(ls);
//for (auto e : lt)
//{
// cout << e << " ";
//}
return 0;
}
疑问1：为什么在迭代器当中不需要写深拷贝、析构函数
1、因为迭代器就是希望做到浅拷贝，就是需要拿到地址而不是值，因为迭代器的修改是会影响对象中的内容的
2、因为迭代器并没有申请额外的空间，所以不需要析构，如果写了析构函数，那么调用一次迭代器那岂不是把对象都给销毁了😂😂😂
疑问2：为什么在迭代器当中需要三个模板参数？
其实这三个参数是被抽象出来的，__list_iterator<T, Ref, Ptr>等价于__list_iterator<T, T&, T>，其实在迭代器当中只有一个参数也可以正常推导，但是在list类当中只有一个参数就不行了，因为如果传递过来的是const修饰的类，然后用T&来接收的话会导致权限被缩小了，所以，为了解决这个const的问题，直接显示的定义模板参数*
typedef __list_iterator<T, T&, T> iterator;
typedef __list_iterator<T, const T&,const T> const_iterator;**Ref就是reference
Ptr就是pointer
疑问3：反向迭代器是怎么实现的？
反向迭代器其实就是利用正向迭代器实现的，重载一下++、–等操作符，不过逻辑上功能要反过来写
疑问4：为什么*解引用不直接返回当前值
因为begin()和end()的位置和正常实现的不一样
文章来源：https://www.toymoban.com/news/detail-532686.html
为什么要加一些不认识的typedef
typedef bidirectional_iterator_tag iterator_category;
typedef T value_type;
typedef Ptr pointer;
typedef Ref reference;
typedef ptrdiff_t difference_type;
我也不知道，不加过不了编译，我太菜了😭😭😭😭😭😭文章来源地址https://www.toymoban.com/news/detail-532686.html
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