【C++】模拟实现vector

可以把vector看作升级版的数组，可采用下标进行访问，非常高效，大小可动态改变，会自动扩容，数据存储在堆空间上。

成员变量、函数及模板总览

namespace ahunb{template<class T>class vector{public:// Vector的迭代器是一个指针 //typedef T* iterator；typedef const T* const_iterator；/ Iterators /iterator begin()；iterator end()；const_iterator cbegin()；const_iterator cend() const；// construct and destroy vector()；vector(int n, const T& value = T())；template<class InputIterator>vector(InputIterator first, InputIterator last)；vector(const vector<T>& v)；vector<T>& operator= (vector<T> v)；~vector()；/ capacity /size_t size() const ；size_t capacity() const；void reserve(size_t n)；void resize(size_t n, const T& value = T())；///Element access//T& operator[](size_t pos)；const T& operator[](size_t pos)const；///modifiers/void push_back(const T& x)；void pop_back()；void swap(vector<T>& v)；iterator insert(iterator pos, const T& x)；iterator erase(Iterator pos)；private:iterator _start; // 指向数据块的开始iterator _finish; // 指向有效数据的尾iterator _endOfStorage; // 指向存储容量的尾};

---

构造函数和析构函数

无参构造函数

vector()
{}

构造n个元素大小的空间并初始化

vector(int n, const T& value = T())
{resize(n);for (int i = 0; i < n; i++){vector[i] = value;}
}

通过某个对象的两个迭代器来构造

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);}
}

赋值运算符重载

vector<T>& operator= (vector<T> v)
{swap(v);return *this;
}

析构函数

~vector()
{delete[] _start;_start = _finish = _endofstorage = nullptr;
}

---

迭代器

返回第一个元素迭代器

多提供一个加const的 ，以防有const对象要调用

iterator begin()
{return _start;
}
const_iterator begin() const
{return _start;
}

返回最后一个元素迭代器

iterator end()
{return _finish;
}
const_iterator end() const
{return _finish;
}

容量和大小相关函数

返回当前大小

size_t size()
{return _finish - _start;
}
const size_t size() const 
{return _finish - _start;
}

返回当前容量上限

size_t capacity()
{return _endofstorage - _start;
}const size_t capacity() const
{return _endofstorage - _start;
}

reserve函数

改变vector的capacity（容量）变量

当n>capacity将capacity改为n，否则不变

对新空间进行拷贝时要深拷贝，否则delete时会出现野指针

void reserve(size_t n)
{if (n > capacity()){int sz = size();iterator tmp = new T[n];if (_start){for (int i = 0; i < sz; i++){tmp[i] = _start[i];//注意使用深拷贝}delete[]  _start;}_start = tmp;_finish = _start + sz;_endofstorage = _start+n;}
}

resize函数

改变vector的size（当前大小）变量

当n>size时，将大小改为n，并将新增加的大小初始化

否则直接将大小改为n就可以

void resize(size_t n, const T& value = T())
{if (n > size()){reserve(n);while (_finish < _start + n){*_finish = value;_finish++;}}else{_finish = _start + n;}
}

---

访问元素接口

[ ]运算符重载

T& operator[](size_t pos)
{assert(pos < size());return _start[pos];
}const T& operator[](size_t pos)const
{assert(pos < size());return _start[pos];
}

添加元素与删除元素

尾插

void push_back(const T& x)
{if (_finish == _endofstorage){int cp = capacity();cp = (cp == 0 ? 4 : cp * 2);reserve(cp);}*_finish = x;++_finish;
}

指定位置插入元素

• 注意扩容之后会存在pos失效问题，因为扩容之后原对象改变了_start等指针，指向了新的区间，但pos指向的还是原来的区间，所以在第七行和第九行对pos进行了更新。

iterator insert(iterator pos, const T& x)
{assert(pos <= finish);assert(pos >= _start);if (_finish == _endofstorage){int n = pos - _start;reserve(capacity() + 1);pos = _start + n;}iterator end = _finish;while (end > pos){*end = *(end - 1);end--;}*pos = x;_finish++;return pos;
}

删除指定位置元素

iterator erase(iterator pos)
{assert(pos < finish);assert(pos >= _start);if (_finish - 1 != pos){iterator begin = pos;while (begin < _finish - 1){*begin = *(begin + 1);}}_finish--;return pos+1;
}

尾删

void pop_back()
{erase(_finish - 1);
}

交换

void swap(vector<T>& v)
{std::swap(_start, v._start);std::swap(_finish, v._finish);std::swap(_endofstorage, v._endofstorage);
}

---

源代码

//vector.h
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <assert.h>using namespace std;namespace ahu 
{template <class T>class vector {public:typedef T* iterator;typedef const T* const_iterator;vector(){}vector(int n, const T& value = T()){resize(n);for (int i = 0; i < n; i++){vector[i] = 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;}//Iteratoriterator begin(){return _start;}iterator end(){return _finish;}const_iterator begin() const{return _start;}const_iterator end() const{return _finish;}//Capacitysize_t size(){return _finish - _start;}const size_t size() const {return _finish - _start;}size_t capacity(){return _endofstorage - _start;}const size_t capacity() const{return _endofstorage - _start;}void reserve(size_t n){if (n > capacity()){int sz = size();iterator tmp = new T[n];if (_start){for (int 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()){reserve(n);while (_finish < _start + n){*_finish = value;_finish++;}_finish = _start + n;}else{_finish = _start + n;}}//Element accessT& operator[](size_t pos){assert(pos < size());return _start[pos];}const T& operator[](size_t pos)const{assert(pos < size());return _start[pos];}//Modifiersvoid push_back(const T& x){if (_finish == _endofstorage){int cp = capacity();cp = (cp == 0 ? 4 : cp * 2);reserve(cp);}*_finish = x;++_finish;}void pop_back(){erase(_finish - 1);}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){assert(pos <= finish);assert(pos >= _start);if (_finish == _endofstorage){int n = pos - _start;reserve(capacity() + 1);pos = _start + n;}iterator end = _finish;while (end > pos){*end = *(end - 1);end--;}*pos = x;_finish++;return pos;}iterator erase(iterator pos){assert(pos < finish);assert(pos >= _start);if (_finish - 1 != pos){iterator begin = pos;while (begin < _finish - 1){*begin = *(begin + 1);}}_finish--;return pos+1;}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};
}//vector.cpp
#define _CRT_SECURE_NO_WARNINGS
#include "vector.h"
//#include <vector>
using namespace ahu;
int main()
{vector<int> v1;v1.push_back(1);v1.push_back(1);v1.push_back(1);v1.push_back(1);v1.push_back(1);v1.push_back(1);v1.push_back(1);v1.push_back(1);//v1.push_back(1);vector<int> v2(v1);for (size_t i = 0; i < v2.size(); i++){cout << v2[i] << endl;}cout << "-------------------------------------" << endl;//v2.reserve(100);//cout << v2.capacity() << endl;//cout << v2.size()<<endl;//v2.resize(50);//cout << v2.capacity() << endl;//cout << v2.size() << endl;//v2.reserve(25);//cout << v2.capacity() << endl;//cout << v2.size() << endl;v2.insert(v2.begin()+3, 100);for (size_t i = 0; i < v2.size(); i++){cout << v2[i] << endl;}cout << "-------------------------------------" << endl;v2.erase(v2.begin() + 9);v2.erase(v2.begin() + 8);v2.erase(v2.begin() + 7);v2.erase(v2.begin() + 6);v2.erase(v2.begin() + 5);v2.erase(v2.begin() + 4);v2.erase(v2.begin()+3);for (size_t i = 0; i < v2.size(); i++){cout << v2[i] << endl;}
}

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