C++vector部分实现及感悟

myvector.h
#pragma once
#include<assert.h>
#include<iostream>
#include<vector>
using namespace std;
namespace bit {template<class T>//必须使用typename场景\template<typename T>与template<class T>一般情况下这两个通用，但有一个特例，就是当 T 是一个类，而这个类又有子类(假设名为 innerClass) 时，应该用 template<typename>:\typename T::innerClass myInnerObject; 这里的 typename 告诉编译器，T::innerClass 是一个类，程序要声明一个 T::innerClass 类的对象，而不是声明 T 的静态成员，而 typename 如果换成 class 则语法错误。class vector{public:typedef T* iterator;typedef const T* const_iterator;//const指针得到const迭代器，非const得非const迭代器const_iterator begin()const{return _start;}const_iterator end()const{return _end;}iterator begin(){return _start;}iterator end(){return _end;}// 类模板的成员函数
// 函数模板 -- 目的支持任意容器的迭代器区间初始化template<class InputIterator>vector(InputIterator it_begin, InputIterator it_end){while (it_begin != it_end){push_back(*(it_begin++));}}vector() = default;vector(size_t n, const T& val = T()){reserve(n);//尽量一次性开空间for (size_t i = 0; i < n; i++)//和n同一类型大小push_back(val);}vector(initializer_list<T> il){reserve(il.size());//要push_back,insert等频繁插入数据就想优化一次插入for (auto& e : il)//初始列表支持迭代器就支持范围for从头往后{push_back(e);}}vector(int n, const T& val = T())//要有int版本的不然传两个数字为int与迭代器模板函数混淆{reserve(n);//尽量一次性开空间for (int i = 0; i < n; i++)//和n同一类型大小push_back(val);}vector(const vector<T>& v){//拷贝构造实现深度拷贝reserve(v.capacity());for (auto& e : v){push_back(e);}}void swap(vector<T>&v){std::swap(this->_start, v._start);std::swap(this->_end, v._end);std::swap(this->_end_of_storage, v._end_of_storage);}vector<T>& operator=(vector<T> v)//现代写法，可以传参的拷贝实参，深拷贝再交换自动析构{swap(v);return *this;//可以连续运算的返回其值}~vector(){if (_start){delete[] _start;_start = _end_of_storage = _end = nullptr;}}void reserve(size_t n)//size_t{//不能用memcpy拷贝新旧空间，浅拷贝的空间会析构两次if (n > capacity()){size_t oldsizes = size();iterator new_start = new T[n];for (size_t i = 0; i < oldsizes; i++){new_start[i] = _start[i];}delete[] _start;_start = new_start;_end = _start + oldsizes;_end_of_storage = _start+n;}}size_t capacity()const //仅访问的允许常this指针{return _end_of_storage - _start;}size_t size()const{return _end - _start;}T& operator[](size_t n){assert(n < size());//访问越界检查return _start[n];}const T& operator[](size_t n)const//常指针访问返回常引用[]{assert(n < this->size());return _start[n];}void push_back(const T& val){//if (_end == _end_of_storage)//{//	size_t capacity = capacity() == 0 ? 4 : 2 * capacity();//	reserve(capacity);//}//*_end++ = val;//后置++优先级大于解引用insert(end(), val);}void popback(){assert(size());--_end;}iterator insert(iterator pos, const T& val)//pos迭代器不能传引用，不然外部不能拷贝传参临时变量引用，insert(t.begin()->传的临时变量不能传普通引用{//这里形参如果是引用的话，则编译时会报错，因为v.begin()返回的是一个临时变量，自定义类型传值拷贝返回，返回临时变量再拷贝给接收的，是一个右值，它不能赋值给一个非const的引用： assert(pos <= _end);assert(pos >= _start);if (_end == _end_of_storage){size_t len = pos - _start;size_t capacity = this->capacity() == 0 ? 4 : this->capacity() * 2;reserve(capacity);pos = _start + len;//内部迭代器更新}iterator end = _end-1;while (end >= pos){*(end + 1)=*end;end--;}_end++;*pos = val;return pos;}iterator erase(iterator pos){assert(pos < _end);assert(pos >= _start);iterator pos_i = pos+1;while (pos_i < _end)*(pos_i - 1) = *pos_i++;--_end;return pos;}private://在类型定义后写iterator _start = nullptr;iterator _end = nullptr;iterator _end_of_storage = nullptr;};
}
void test01()
{bit::vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);size_t size = v1.size();for (int i = 0; i < size; i++)cout << v1[i] << endl;for (const auto& e : v1)cout << e << endl;bit::vector<int>::iterator it_begin = v1.begin();bit::vector<int>::iterator it_end = v1.end();for (; it_begin < it_end; it_begin++)cout << *it_begin << endl;}void test02()
{bit::vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);v1.insert(v1.begin(), 0);size_t size = v1.size();for (int i = 0; i < size; i++)cout << v1[i] << " ";cout << endl;for (const auto& e : v1)cout << e << " ";cout << endl;v1.erase(v1.end() - 1);bit::vector<int>::iterator it_begin = v1.begin();bit::vector<int>::iterator it_end = v1.end();for (; it_begin < it_end; it_begin++)cout << *it_begin << " ";cout << endl;int x;cin >> x;bit::vector<int>::iterator pos_x = find(v1.begin(), v1.end(), x);//模板实例化才能找类域if (pos_x != v1.end()){pos_x =v1.insert(pos_x, 1000);// 建议失效后迭代器不要访问。除非赋值 更新 一下这个失效的迭代器cout << *pos_x << endl;}for (const auto& e : v1)cout << e << " ";cout << endl;}
void test03()
{std::vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);int x;cin >> x;std::vector<int>::iterator it = find(v1.begin(), v1.end(), x);if (it != v1.end()){// erase it以后，it是否失效呢？失效it = v1.erase(it);if (it != v1.end())cout << *it << endl;}cout << typeid(it).name() << endl;
}
void test_vector4()
{std::vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);std::vector<int>::iterator it = v1.begin();while (it < v1.end())//用迭代器遍历并删除偶数{if (*it % 2 == 0){it = v1.erase(it);}else++it;}for (auto e : v1){cout << e << " ";}cout << endl;
}
void test_vector5()
{bit::vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);bit::vector<int> v2(v1);for (auto e : v2){cout << e << " ";}cout << endl;bit::vector<int> v3;v3.push_back(10);v3.push_back(20);v3.push_back(30);v1 = v3;for (auto e : v1){cout << e << " ";}cout << endl;
}
void test_vector07()
{int i = int();int k(2);int f = { 3 };int h = int(7);int j{ 1 };
}