【C++】“list”的介绍和常用接口的模拟实现
#include<assert.h>
#include<iostream>
using std::cout;
using std::endl;
namespace wch
{
//由于list中的val支持多种类型，定义模板参数T
template<class T>
struct list_node
{
list_node<T>* _next;
list_node<T>* _prev;
T _val;
//T(),针对自定义类型会去调用它的构造函数，针对内置类型无影响
list_node(const T& val = T())
:_next(nullptr)
, _prev(nullptr)
, _val(val)
{}
};
// typedef __list_iterator<T, T&, T*> iterator;
// typedef __list_iterator<T, const T&, const T*> const_iterator;
//此处定义多个模板参数针对返回值类型
template<class T, class Ref, class Ptr>
struct __list_iterator
{
typedef list_node<T> Node;
typedef __list_iterator<T, Ref, Ptr> self;
Node* _node;
__list_iterator(Node* node)
:_node(node)
{}
Ref operator*() const//重载普通对象解引用
{
return _node->_val;
}
Ptr operator->() const//重载指针对象解引用
{
return &_node->_val;
}
self& operator++()//返回对象在函数体执行结束后依旧存在，建议引用返回，减少拷贝开销
{
_node = _node->_next;
return *this;
}
//返回对象（局部变量或指向局部变量的指针）在函数体执行结束后不存在，不可引用返回，值返回
self operator++(int)
{
self tmp(*this);
_node = _node->_next;
return tmp;
}
self& operator--()
{
_node = _node->_prev;
return *this;
}
self operator--(int)
{
self tmp(*this);
_node = _node->_prev;
return tmp;
}
//尽量使用引用形参， 避免拷贝开销。同时在不需要修改实参时，通过指定const 引用形参来限制。
bool operator!=(const self& it) const
{
return _node != it._node;
}
bool operator==(const self& it) const
{
return _node == it._node;
}
};
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;
// 这样设计const迭代器是不行的，因为const迭代器期望指向内容不能修改
// 这样设计是迭代器本身不能修改
// T* const ptr2;
iterator begin()
{
//return _head->_next;//单参构造函数支持隐式类型转换
return iterator(_head->_next);
}
iterator end()
{
return _head;//单参构造函数支持隐式类型转换
//return iterator(_head);
}
const_iterator begin() const
{
//return _head->_next;
return const_iterator(_head->_next);
}
const_iterator end() const
{
return _head;
//return const_iterator(_head);
}
void empty_init()
{
_head = new Node;
_head->_prev = _head;
_head->_next = _head;
_size = 0;
}
list()//无参默认构造函数
{
empty_init();
}
// lt2(lt1)
list(const list<T>& lt)//拷贝构造
//list(const list& lt)//不加类型也可以，不建议
{
empty_init();
for (auto& e : lt)//深拷贝
{
push_back(e);
}
}
void swap(list<T>& lt)
{
std::swap(_head, lt._head);
std::swap(_size, lt._size);
}
list<T>& operator=(list<T> lt)//赋值运算符重载
//list& operator=(list lt)//不加类型也可以，不建议
{
swap(lt);
return *this;
}
~list()//析构函数
{
clear();
delete _head;
_head = nullptr;
}
void clear()
{
iterator it = begin();
while (it != end())
{
it = erase(it);//带位置返回值的erase函数，防止迭代器失效
}
_size = 0;
}
void push_back(const T& x)
{
insert(end(), x);
}
void push_front(const T& x)
{
insert(begin(), x);
}
void pop_back()
{
erase(--end());
}
void pop_front()
{
erase(begin());
}
// pos位置之前插入
iterator insert(iterator pos, const T& x)
{
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* newnode = new Node(x);
prev->_next = newnode;
newnode->_next = cur;
cur->_prev = newnode;
newnode->_prev = prev;
++_size;
return newnode;
}
//删除pos处节点
iterator erase(iterator pos)
{
assert(pos != end());//不可删除头节点
Node* cur = pos._node;
Node* prev = cur->_prev;
Node* next = cur->_next;
prev->_next = next;
next->_prev = prev;
delete cur;
--_size;
return next;
}
size_t size()
{
/*size_t sz = 0;
iterator it = begin();
while (it != end())
{
++sz;
++it;
}
return sz;*/
return _size;
}
private:
Node* _head;
size_t _size;
};
void Print(const list<int>& lt)
{
list<int>::const_iterator it = lt.begin();
while (it != lt.end())
{
//(*it) += 1;
cout << *it << " ";
++it;
}
cout << endl;
}
void test_list1()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
list<int>::iterator it = lt.begin();
//由于链表的各个节点地址是不连续的，前一个节点的地址可能比后一个地址大，所以不可已写为 it < it.end();
while (it != lt.end())
{
(*it) += 1;
cout << *it << " ";
++it;
}
cout << endl;
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
Print(lt);
}
struct A
{
A(int a1 = 0, int a2 = 0)
:_a1(a1)
, _a2(a2)
{}
int _a1;
int _a2;
};
void test_list2()
{
list<A> lt;
lt.push_back(A(1, 1));
lt.push_back(A(2, 2));
lt.push_back(A(3, 3));
lt.push_back(A(4, 4));
list<A>::iterator it = lt.begin();
while (it != lt.end())
{
//cout << (*it)._a1 << " " << (*it)._a2 << endl;
//it->->_a1, it->->_a2,特殊处理为一个->
cout << it->_a1 << " " << it->_a2 << endl;
++it;
}
cout << endl;
}
void test_list3()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
lt.push_front(5);
lt.push_front(6);
lt.push_front(7);
lt.push_front(8);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
lt.pop_front();
lt.pop_back();
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
lt.clear();
lt.push_back(10);
lt.push_back(20);
lt.push_back(30);
lt.push_back(40);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
cout << lt.size() << endl;
}
void test_list4()
{
list<int> lt;
lt.push_back(1);
lt.push_back(2);
lt.push_back(3);
lt.push_back(4);
for (auto e : lt)
{
cout << e << " ";
}
cout << endl;
list<int> lt1(lt);
for (auto e : lt1)
{
cout << e << " ";
}
cout << endl;
list<int> lt2;
lt2.push_back(5);
lt2.push_back(6);
lt2.push_back(7);
lt2.push_back(8);
for (auto e : lt2)
{
cout << e << " ";
}
cout << endl;
lt1 = lt2;
for (auto e : lt1)
{
cout << e << " ";
}
cout << endl;
}
}