对于实现reverse_iterator，我们可以学栈和队列的实现过程，利用适配器，实现如下;
cpp
#pragma once
template<class Iterator,class Ref,class Ptr>
class reverse_Iterator
{
public:
//构造函数：
reverse_Iterator(Iterator it)
:_it(it)
{}
typedef reverse_Iterator<Iterator, Ref, Ptr> Self;
//操作：
bool operator!=(const Self& cur)
{
return !(_it == cur._it);
}
bool operator==(const Self& cur)
{
return _it == cur._it;
}
Self& operator++()
{
_it--;
return *this;
}
Self operator++(int)
{
Self tmp(*this);
_it--;
return tmp;
}
Self& operator--()
{
_it++;
return *this;
}
Self operator--(int)
{
Self tmp(*this);
_it++;
return tmp;
}
Ref operator*()
{
//解引用是找前一个：
Iterator tmp = _it;
return *(--tmp);
}
Ptr operator&()
{
//取地址也是找前一个：
return &(operator*());
}
private:
Iterator _it;
};此时我们将实现的reverse_iterator添加到vector和list上如下：
（注意：vector、list其余部分之前已经实现过了）
vector.h
cpp
#pragma once
#include <assert.h>
#include <iostream>
#include <string.h>
#include "reverse_iterator.h"
namespace cx
{
//模板类
template<class T>
class vector
{
public:
typedef T* iterator;
typedef const T* const_iterator;
typedef reverse_Iterator<iterator, T&, T*> reverse_iterator;
typedef reverse_Iterator<const_iterator, const T&, const T*> const_reverse_iterator;
//构造函数:
vector()
{}
//传统写法
/*vector(const vector<T>& v)
{
_start = new T[v.capacity()];
memcpy(_start, v._start, v.size() * sizeof(T));
_finish = _start + v.size();
_endofstorage = _start + v.capacity();
}*/
//现代写法：
vector(const vector<T>& v)
{
reserve(v.capacity());
for (const auto e : v)
{
*_finish = e;
_finish++;
}
}
vector(size_t n, const T& val = T())
{
resize(n,val);
}
/*template <class InputIterator>
vector(InputIterator first, InputIterator last)
{
while (first != last)
{
push_back(*first);
first++;
}
}*/
//析构函数
~vector()
{
if (_start)
{
delete[] _start;
_start = _finish = _endofstorage = nullptr;
}
}
vector<T>& operator=(vector<T> v)
{
swap(v);
return *this;
}
//迭代器
iterator begin()
{
return _start;
}
iterator end()
{
return _finish;
}
const_iterator begin()const
{
return _start;
}
const_iterator end()const
{
return _finish;
}
reverse_iterator rend()
{
return _start;
}
reverse_iterator rbegin()
{
return _finish;
}
const_reverse_iterator crend()const
{
return _start;
}
const_reverse_iterator crbegin()const
{
return _finish;
}
//计算大小
size_t size()const
{
return end() - begin();
}
size_t capacity()const
{
return _endofstorage - _start;
}
//操作:
bool empty() const
{
return _finish == _start;
}
void swap(vector<T>& v)
{
std::swap(_start, v._start);
std::swap(_finish, v._finish);
std::swap(_endofstorage, v._endofstorage);
}
void reserve(size_t n)
{
if (n > capacity())
{
size_t old = size();
T* tmp = new T[n];
if (_start)
{
memcpy(tmp, _start, sizeof(T) * old);
delete[] _start;
}
_start = tmp;
_finish = _start + old;
_endofstorage = _start + n;
}
}
void push_back(const T x)
{
//检查是否扩容
if (_finish == _endofstorage)
{
size_t newcapacity = capacity() == 0 ? 4 : 2 * capacity();
reserve(newcapacity);
}
*_finish = x;
_finish++;
}
void pop_back()
{
assert(size() > 0);
_finish--;
}
T& operator[](size_t pos)
{
assert(pos < size());
return _start[pos];
}
T& operator[] (size_t pos) const
{
assert(pos < size());
return _start[pos];
}
iterator insert(iterator pos, const T& val)
{
assert(pos <= _finish && pos >= _start);
if (_finish == _endofstorage)
{
size_t len = pos - _start;
reserve(capacity() == 0 ? 4 : 2 * capacity());
pos = _start + len;
}
//memmove(pos + 1, pos, sizeof(T) * (_finish - pos));
iterator end = _finish - 1;
while (end >= pos)
{
*(end + 1) = *(end);
end--;
}
*pos = val;
_finish++;
return pos;
}
/*void insert(iterator pos, const T& x)
{
//检查
assert(pos >= _start);
assert(pos <= _finish);
if (_finish == _endofstorage)
{
size_t len = pos - _start;
reserve(capacity() == 0 ? 4 : 2 * capacity());
//注意：pos位置也要改变
pos = _start + len;
}
memmove(pos + 1, pos, sizeof(T) * (_finish - pos));
*pos = x;
_finish++;
}*/
iterator erase(iterator pos)
{
assert(pos < _finish && pos >= _start);
iterator it = pos + 1;
while (it < _finish)
{
*(it - 1) = *it;
it++;
}
_finish--;
return pos;
}
iterator erase(iterator first, iterator last)
{
}
void resize(size_t n, T val = T())
{
if (n > size())
{
reserve(n);
while (_finish < _start + n)
{
*_finish = val;
_finish++;
}
}
else
{
_finish = _start + n;
}
}
T& front()
{
return *_start;
}
const T& front() const
{
*_start;
}
T& back()
{
return *_finish;
}
const T& back() const
{
return *_finish;
}
T& at(size_t pos)
{
assert(pos < size());
return _start[pos];
}
const T& at(size_t pos) const
{
assert(pos < size());
return _start[pos];
}
void assign(size_t n, const T& val)
{
assert(_start == _finish);
reserve(n);
while (_finish != _endofstorage)
{
*_finish = val;
_finish++;
}
}
void clear()
{
resize(0);
}
private:
iterator _start = nullptr;
iterator _finish = nullptr;
iterator _endofstorage = nullptr;
};
}list.h:
cpp
#pragma once
#include <assert.h>
#include "reverse_iterator.h"
namespace cx
{
template <class T>
struct ListNode
{
//构造函数
ListNode(const T& x=T())
:_next(nullptr),_prev(nullptr),_val(x)
{}
//成员变量：
ListNode<T>* _next;
ListNode<T>* _prev;
T _val;
};
template <class T,class Ref,class Ptr>
//template <class T, class Ref>
struct _list_iterator
{
typedef ListNode<T> Node;
typedef _list_iterator<T,Ref, Ptr> self;
//typedef _list_iterator<T, Ref> self;
//构造函数：
//_list_iterator()
/*iterator(Node* x)
:_node(x)
{}*/
_list_iterator(Node* x)
:_node(x)
{}
//不用写析构：原因在于我们的目标不是在这里析构
//常见操作：
self& operator++()//前置++
{
_node = _node->_next;
return (*this);
}
self operator++(int)//后置++
{
self tmp(*this);
_node = _node->_next;
return tmp;
}
self& operator--()//前置--
{
_node = _node->_prev;
return *this;
}
self operator--(int)//后置--
{
self tmp(*this);
_node = _node->_prev;
return tmp;
}
Ref operator*()
{
return _node->_val;
}
bool operator!=(const self& s)
{
return !(_node == s._node);
}
bool operator==(const self& s)
{
return !(*this != s);
}
Ptr operator->()
{
return &_node->_val;
}
//类成员函数：
Node* _node;
};
//template <class T>
//struct _list_const_iterator
//{
// typedef ListNode<T> Node;
// typedef _list_const_iterator<T> const_iterator;
// //构造函数：
// //_list_iterator()
// /*iterator(Node* x)
// :_node(x)
// {}*/
// _list_const_iterator(Node* x)
// :_node(x)
// {}
// //不用写析构：原因在于我们的目标不是在这里析构
// //常见操作：
// const_iterator& operator++()//前置++
// {
// _node = _node->_next;
// return (*this);
// }
// const_iterator operator++(int)//后置++
// {
// const_iterator tmp(*this);
// _node = _node->_next;
// return tmp;
// }
// const_iterator& operator--()//前置--
// {
// _node = _node->_prev;
// return *this;
// }
// const_iterator& operator--(int)//后置--
// {
// const_iterator tmp(*this);
// _node = _node->_prev;
// return tmp;
// }
// const T& operator*()
// {
// return _node->_val;
// }
// bool operator!=(const const_iterator& s)
// {
// return !(_node == s._node);
// }
// bool operator==(const const_iterator& s)
// {
// return !(*this != s);
// }
// //类成员函数：
// Node* _node;
//};
template <class T>
class list
{
public:
typedef ListNode<T> Node;
//typedef _list_iterator<T,T&> iterator;
typedef _list_iterator<T, T&, T*> iterator;
//typedef _list_iterator<T, const T&> const_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;
//构造函数
void empty_list()
{
_head = new Node;
_head->_next = _head;
_head->_prev = _head;
}
list()
{
empty_list();
}
//list ( list& x);
list(const list<T>& s)
{
empty_list();
for (auto e : s)//该类型为：T
{
push_back(e);
}
}
//list& operator= (const list& lt);
//传统写法：
//list<T>& operator= (list<T>& lt)
//{
// if(this != <)
// {
// //清除*this中内容
// clear();
// for (T e : lt)
// {
// push_back(e);
// }
// }
// return *this;
//}
//现代写法：
list<T>& operator= (list<T> lt)
{
swap(lt);
return *this;
}
//析构函数：
void clear()
{
//区别析构函数，clear只会删除有效数据，保留虚拟头结点
iterator it = begin();
while (it != end())
{
it=erase(it);
}
}
~list()
{
clear();
//删除_head;
delete _head;
_head = nullptr;
}
//迭代器：
iterator begin()//有效第一个节点
{
//assert(_head->_next != _head);
//如果写上面这句，会出现开始为空链表报错情况
return _head->_next;
}
const_iterator begin() const
{
return _head->_next;
}
iterator end()
{
return _head;
}
const_iterator end() const
{
return _head;
}
reverse_iterator rbegin()
{
return reverse_iterator(end());
}
reverse_iterator rend()
{
return reverse_iterator(begin());
}
const_reverse_iterator rbegin()const
{
return const_reverse_iterator(end());
}
const_reverse_iterator rend()const
{
return const_reverse_iterator(begin());
}
//常见操作：
iterator erase(iterator pos)
{
//检查pos位置非_head位置
assert(pos !=end());
//删除的是pos位置
Node* current = pos._node;
Node* prev = current->_prev;
Node* next = current->_next;
//删除操作
prev->_next = next;
next->_prev = prev;
delete current;
return next;//返回的是pos下一个位置
}
iterator erase(iterator first, iterator last)//区间左闭右开
{
assert(first != end());
assert(last != end());
while (first != last)
{
if (first == end())
break;
first = erase(first);
}
return first;
}
void push_back(const T& val)
{
Node* tmp = new Node(val);
Node* tail = _head->_prev;
tail->_next = tmp;
tmp->_prev = tail;
tmp->_next = _head;
_head->_prev = tmp;
}
void swap(list<T>& tmp)
{
std::swap(_head, tmp._head);
}
iterator insert(iterator pos, const T& x)
{
//insert是指在pos位置前插入
Node* current = pos._node;
Node* prev = current->_prev;
//开空间
Node* tmp = new Node(x);
tmp->_prev = prev;
prev->_next = tmp;
tmp->_next = current;
current->_prev = tmp;
//return iterator(tmp);
return tmp;//注意点：单参数的类可以隐式类型转换
}
//容量相关：
bool empty() const
{
return _head->_next == _head;
}
size_t size() const
{
size_t n = 0;
Node* tmp = _head->_next;
while (tmp!=_head)
{
tmp = tmp->_next;
n++;
}
return n;
}
void push_front(const T& x)
{
this->insert(begin(), x);
}
void pop_back()
{
this->erase(--end());
}
void pop_front()
{
erase(begin());
}
//Element access:
T& front()
{
return _head->_next->_val;
}
const T& front() const
{
return _head->_next->_val;
}
T& back()
{
return _head->_prev->_val;
}
const T& back() const
{
return _head->_prev->_val;
}
private:
//虚拟头结点：
Node* _head;
};
}这里再给大家一组测试用例：
cpp
#include <iostream>
using namespace std;
#include "vector.h"
#include "list.h"
void test_list()
{
cx::list<int> l;
l.push_back(1);
l.push_back(2);
l.push_back(3);
l.push_back(4);
l.push_back(5);
l.push_back(6);
cx::list<int>::reverse_iterator it = l.rbegin();
while (it != l.rend())
{
cout << *it << " ";
it++;
}
cout << endl;
}
void test_vector()
{
cx::vector<int> l;
l.push_back(1);
l.push_back(2);
l.push_back(3);
l.push_back(4);
l.push_back(5);
l.push_back(6);
cx::vector<int>::reverse_iterator it = l.rbegin();
while (it != l.rend())
{
cout << *it << " ";
it++;
}
cout << endl;
}
int main()
{
test_list();
test_vector();
return 0;
}感谢大家的支持！！！