🎬慕斯主页：修仙—别有洞天
♈️今日夜电波：くちなしの言葉—みゆな
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目录
一、vector实际的底层原理
class vector
{
public:
typedef T* iterator;
typedef const T* const_iterator;
private:
iterator _start;
iterator _finish;
iterator _endofstorage;
};配合图解明白：
二、vector的模拟实现
迭代器相关
// Vector的迭代器是一个原生指针
typedef T* iterator;
typedef const T* const_iterator;
iterator begin()
{
return _start;
}
iterator end()
{
return _finish;
}
const_iterator begin() const
{
return _start;
}
const_iterator end() const
{
return _finish;
}基本操作（迭代器失效问题）
插入
iterator insert(iterator pos, const T& x)//迭代器失效，返回新的迭代器解决
{
assert(pos >= _start);
assert(pos <= finish);
if (_finish == _endOfStorage)
{
size_t len = pos - _start;//避免位置错误,因为在扩容后_start的地址会变化
reserve(capacity() == 0 ? 4 : capacity() * 2);
pos = start + len;//恢复位置
}
iterator end = _finish - 1;
while (end >= pos)//从后往前挪
{
*(end + 1) = *end;
--end;
}
*pos = x;
++_finish;
return pos;
}
删除
iterator erase(Iterator pos)//迭代器失效，返回新的迭代器解决
{
assert(pos >= _start);
assert(pos < _finish);
iterator it = pos + 1;//定义一个变量用于删除
while (it < _finish)
{
*(it - 1) = *it;
++it;
}
--_finish;
return pos;
}push_back（）
void push_back(const T& x)
{/*
if (_finish == _endofstorage)
{
reserve(capacity() == 0 ? 4 : capacity() * 2);
}
*_finish = x;
++_finish;*/
insert(end(), x);
}pop_back（）
void pop_back()
{
assert(!empty());
--_finish;
}swap（）
void swap(vector<T>& v)
{
std::swap(_start, v._start);
std::swap(_finish, v._finish);
std::swap(_endofstorage, v._endofstorage);
}基本成员函数
构造函数
vector()
:_start(nullptr)
,_finish(nullptr)
,_endOfStorage(nullptr)
{}
vector()
{}
vector(int n, const T& value = T())
{
reserve(n);
for (int i = 0; i < n; i++)
{
push_back(value);
}
}
template<class InputIterator>
vector(InputIterator first, InputIterator last)
{
while (first != last)
{
push_back(*first);
++first;
}
}
拷贝构造函数
vector(const vector<T>& v)
{
reserve(v.capacity());
for (auto& e : v)
{
push_back(e);
}
}析构函数
~vector()
{
delete[] _start;
_start = _finish = _endofstorage = nullptr;
}赋值运算符
vector<T>& operator= (vector<T> v)
{
swap(v);
return *this;
}空间管理
基本状态
size_t capacity() const
{
return _endofstorage - _start;
}
size_t size() const
{
return _finish - _start;
}
bool empty()const
{
return size() == 0;
}扩容操作
void reserve(size_t n)
{
if (n > capacity())
{
T* tmp = new T[n];
size_t sz = size();
if (_start)
{
//memcpy(tmp, _start, sizeof(T) * sz)//这里用memcpy这里会导致string的vector出错，浅拷贝问题
for (size_t i = 0; i < sz; i++)
{
tmp[i] = _start[i];
}
delete[] _start;
}
_start = tmp;
_finish = _start + sz;
_endOfStorage = _start + n;
}
}resize（）
void resize(size_t n, const T& value = T())
{
if (n < size())
{
_finish =_start + n;
}
else
{
reserve(n);
while (_finish < _start + n)
{
*_finish = val;
++_finish;
}
}
}重载[ ]（最爱的运算符！！！）
T& operator[](size_t pos)
{
assert(pos < size());
return _start[pos];
}
const T& operator[](size_t pos)const
{
assert(pos < size());
return _start[pos];
}三、整体代码
#pragma once
#define _CRT_SECURE_NO_WARNINGS 01
#include<iostream>
using namespace std;
namespace lt
{
template<class T>
class vector
{
public:
// Vector的迭代器是一个原生指针
typedef T* iterator;
typedef const T* const_iterator;
iterator begin()
{
return _start;
}
iterator end()
{
return _finish;
}
const_iterator begin() const
{
return _start;
}
const_iterator end() const
{
return _finish;
}
// construct and destroy
vector()
:_start(nullptr)
,_finish(nullptr)
,_endOfStorage(nullptr)
{}
vector(int n, const T& value = T())
{
reserve(n);
for (int i = 0; i < n; i++)
{
push_back(value);
}
}
template<class InputIterator>
vector(InputIterator first, InputIterator last)
{
while (first != last)
{
push_back(*first);
++first;
}
}
vector(const vector<T>& v)
{
reserve(v.capacity());
for (auto& e : v)
{
push_back(e);
}
}
vector<T>& operator= (vector<T> v)
{
swap(v);
return *this;
}
~vector()
{
delete[] _start;
_start = _finish = _endofstorage = nullptr;
}
// capacity
size_t capacity() const
{
return _endofstorage - _start;
}
size_t size() const
{
return _finish - _start;
}
bool empty()const
{
return size() == 0;
}
void reserve(size_t n)
{
if (n > capacity())
{
T* tmp = new T[n];
size_t sz = size();
if (_start)
{
//memcpy(tmp, _start, sizeof(T) * sz)//这里用memcpy这里会导致string的vector出错，浅拷贝问题
for (size_t i = 0; i < sz; i++)
{
tmp[i] = _start[i];
}
delete[] _start;
}
_start = tmp;
_finish = _start + sz;
_endOfStorage = _start + n;
}
}
void resize(size_t n, const T& value = T())
{
if (n < size())
{
_finish =_start + n;
}
else
{
reserve(n);
while (_finish < _start + n)
{
*_finish = val;
++_finish;
}
}
}
///access///
T& operator[](size_t pos)
{
assert(pos < size());
return _start[pos];
}
const T& operator[](size_t pos)const
{
assert(pos < size());
return _start[pos];
}
///modify/
void push_back(const T& x)
{/*
if (_finish == _endofstorage)
{
reserve(capacity() == 0 ? 4 : capacity() * 2);
}
*_finish = x;
++_finish;*/
insert(end(), x);
}
void pop_back()
{
assert(!empty());
--_finish;
}
void swap(vector<T>& v)
{
std::swap(_start, v._start);
std::swap(_finish, v._finish);
std::swap(_endofstorage, v._endofstorage);
}
iterator insert(iterator pos, const T& x)//迭代器失效，返回新的迭代器解决
{
assert(pos >= _start);
assert(pos <= finish);
if (_finish == _endOfStorage)
{
size_t len = pos - _start;//避免位置错误,因为在扩容后_start的地址会变化
reserve(capacity() == 0 ? 4 : capacity() * 2);
pos = start + len;//恢复位置
}
iterator end = _finish - 1;
while (end >= pos)//从后往前挪
{
*(end + 1) = *end;
--end;
}
*pos = x;
++_finish;
}
iterator erase(Iterator pos)//迭代器失效，返回新的迭代器解决
{
assert(pos >= _start);
assert(pos < _finish);
iterator it = pos + 1;//定义一个变量用于删除
while (it < _finish)
{
*(it - 1) = *it;
++it;
}
--_finish;
return pos;
}
private:
iterator _start = nullptr; // 指向数据块的开始
iterator _finish = nullptr; // 指向有效数据的尾
iterator _endOfStorage = nullptr; // 指向存储容量的尾
};
}
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