一：C++库中对于vector的介绍
vector的底层其实就是数据结构中的顺序表，顺序表的底层就是变长数组，是一段连续的物理空间
在下面的实现中，重点实现的是其中的迭代器和插入删除，下标访问等功能，模拟实现模板类，有利于加深对于模板的认识，更方便使用
二：模拟实现
在模拟实现过程中，要注意迭代器失效问题
#pragma once
#include <iostream>
#include <assert.h>using namespace std;namespace Zq
{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 destroyvector():_start(nullptr),_finish(nullptr),_endOfStorage(nullptr){}vector(int n, const T& value = T()){for (size_t i = 0; i < n; i++){push_back(value);}}template<class InputIterator>vector(InputIterator first, InputIterator last){auto it = first;while (it != last){push_back(*it);it++;}}vector(const vector<T>& v){vector tmp(v.begin(), v.end());swap(tmp);}vector<T>& operator= (vector<T> v){swap(v);return *this;}~vector(){delete[] _start;_finish = _start = _endOfStorage = nullptr;}// capacitysize_t size() const{return _finish - _start;}size_t capacity() const{return _endOfStorage - _start;}//扩容void reserve(size_t n){if (capacity() < n){size_t oldsize = size();T* tmp = new T[n];memcpy(tmp, _start, sizeof(T) * oldsize);delete[] _start;_start = tmp;_finish = _start + oldsize;_endOfStorage = _start + n;}}//开空间，并初始化void resize(size_t n, const T& value = T()){_start = new T[n];_finish = _start;_endOfStorage = _start + n;for (size_t i = 0; i < n; i++){push_back(value);}}///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){insert(end(), x);}void pop_back(){erase(end()-1);}void swap(vector<T>& v){std::swap(_start, v._start);std::swap(_finish, v._finish);std::swap(_endOfStorage, v._endOfStorage);}//注意迭代器失效iterator insert(iterator pos, const T& x){assert(pos <= _finish);assert(pos >= _start);if (_finish == _endOfStorage){int newcapacity = capacity() == 0 ? 4 : capacity() * 2;int len = pos - _start;reserve(newcapacity);pos = _start + len;}iterator end = _finish;while (end != pos){*end = *(end - 1);end--;}*pos = x;_finish++;return pos;}iterator erase(iterator pos){assert(pos >= _start);assert(pos < _finish);iterator it = pos;while ((it + 1) != end()){*it = *(it + 1);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};}
