当前位置：首页 > news >正文

【C++】C++的Vector使用和实现

news 来源：原创 2024/9/29 13:03:39

vector的介绍

vector的使用

construct

iterator

capacity

Element access

mondifiers

vector的原理介绍以及简单实现

vector的介绍

我们平时在写代码中可能会使用各种类型的array，也就是数组，但是这些数组都是静态的，意味着我们只能一开始就确定他们的大小并且存储固定的数据。但是实际应用中需要动态变化的，数组可能时大时小，因此我们需要了解STL库中的vector容器，我们可以将其看作为动态的顺序表，也就是动态的数组，接下来让我们从使用和探寻底层并且实现三个方面来认识vector！

vector的使用

vector的使用包含多个方面，本次着重于常用的函数，其他的功能大家可以自行了解探寻：vector - C++ Reference (cplusplus.com)

construct

void Test_construct()
{// 无参构造vector<int> v1;// 带参构造vector<int> v2({ 1, 2, 3, 4 });vector<int> v3(1);vector<int> v4(5, 1);// 迭代器构造vector<int> v5(v4.begin(), v4.end());// 拷贝构造vector<int> v6(v5);// 赋值重载vector<int> v7;v7 = v6;
}

iterator

// begin, end
vector<int> v({ 1, 2, 3, 4 });
cout << "正向遍历" << endl;
vector<int>::iterator it = v.begin();
while (it != v.end())
{cout << *it << " ";++it;
}
cout << endl;
// rbegin rend
cout << "反向遍历" << endl;
vector<int>::reverse_iterator rit = v.rbegin();
while (rit != v.rend())
{cout << *rit << " ";++rit;
}

capacity

vector<int> v{ 1, 2, 3, 4, 5 };
// size 显示v中的数据个数
cout << "size:" << v.size() << endl;
// max_size 表示v中最多可以存储多少个数据
cout << "max_size:" << v.max_size() << endl;
// resize 收缩v中的数据到某个个数值
for (auto e : v)
{cout << e << " ";
}
cout << endl;
v.resize(2);
for (auto e : v)
{cout << e << " ";
}
cout << endl;
// resize 如果收缩的值比原本的size大，我们可以初始化他们
v.resize(5);
for (auto e : v)
{cout << e << " ";
}
cout << endl;

cout << v.capacity() << endl;vector<int> tmp;
int old_capacity = tmp.capacity();
cout << "tmp grow:" << old_capacity << endl;
for (int i = 0; i < 100; ++i)
{tmp.push_back(i);if (tmp.capacity() != old_capacity){old_capacity = tmp.capacity();cout << old_capacity << endl;}
}

// empty可以用于判断v中的数据是否为空
if (!v.empty())
{cout << "非空" << endl;
}
else {cout << "空" << endl;
}

Element access

int main()
{// operator[]// 重载了这个[],我们可以通过下标遍历元素vector<int> v{ 1,2,3,4,5,6,7,8,9 };for (int i = 0; i < v.size(); ++i){cout << v[i] << " ";}cout << endl;// front 返回v中第一个元素的引用// back  返回v中最后一个元素的引用cout << v.front() << endl;cout << v.back() << endl;return 0;
}

mondifiers

int main()
{vector<int> v;// push_back 尾插v.push_back(9);v.push_back(8);// pop_back 尾删v.pop_back();// insert 插入v.insert(v.begin(), 10);// erase 删除v.erase(v.end() - 1);// swap 交换vector<int> v1{ 7,8,9 };vector<int> v2{ 1,2,3 };v1.swap(v2);for (auto e : v1){cout << e << " ";}cout << endl;// clear 清空size，capacity不变v.clear();for (auto e : v){cout << e << " ";}return 0;
}

vector的原理介绍以及简单实现

#pragma once
#include <iostream>
#include <assert.h>using namespace std;namespace ouyang
{template<class T>class Vector{typedef T* iterator;typedef const T* const_iterator;public:Vector() = default;Vector(const Vector<T>& v){reserve(v.size());for (auto& e : v){push_back(e);}}template<class InputIterator>Vector(InputIterator first, InputIterator last){while (first != last){push_back(*first);++first;}}Vector(size_t n, const T& val = T()){reserve(n);for (int i = 0; i < n; ++i){push_back(val);}}Vector(int n, const T& val = T()){reserve(n);for (int i = 0; i < n; ++i){push_back(val);}}~Vector(){if (_start){cout << "~Vector()" << endl;delete[] _start;_start = _finish = _end_of_storage = nullptr;}}//写法一：/*Vector<T>& operator=(const Vector<T>& v){if (this != &v){clear();reserve(v.size());for (auto& e : v){push_back(e);}}return *this;}*/// 写法二：Vector<T>& operator=(Vector<T> v){Swap(v);return *this;}void clear(){_finish = _start;}void Swap(Vector<T>& v){swap(_start, v._start);swap(_finish, v._finish);swap(_end_of_storage, v._end_of_storage);}iterator begin(){return _start;}iterator end(){return _finish;}const_iterator begin() const{return _start;}const_iterator end() const{return _finish;}size_t size() const{return _finish - _start;}size_t capacity() const{return _end_of_storage - _start;}bool empty(){return _start == _finish;}void reserve(size_t n){if (n > capacity()){size_t oldsize = size();T* tmp = new T[n];memcpy(tmp, _start, sizeof(T) * size());delete[] _start;_start = tmp;_finish = tmp + oldsize;_end_of_storage = tmp + n;}}iterator insert(iterator pos, const T& val){assert(pos >= _start);assert(pos <= _finish);if (_finish == _end_of_storage){size_t len = pos - _start;reserve(capacity() == 0 ? 4 : capacity() * 2);pos = _start + len;}iterator end = _finish - 1;while (end >= pos){*(end + 1) = *end;--end;}*pos = val;++_finish;return pos;}void erase(iterator pos){assert(pos >= _start);assert(pos < _finish);iterator it = pos + 1;while (it != end()){*(it - 1) = *it;++it;}--_finish;}void push_back(const T& val){if (_finish == _end_of_storage){reserve(capacity() == 0 ? 4 : capacity() * 2);}*_finish = val;++_finish;}void pop_back(){assert(!empty());--_finish;}T& operator[](size_t i){assert(i < size());return _start[i];}const T& operator[](size_t i) const{assert(i < size());return _start[i];}private:iterator _start = nullptr;iterator _finish = nullptr;iterator _end_of_storage = nullptr;};template<class Container>
void Print(const Container& object)
{/*auto it = object.begin();while (it != object.end()){cout << *it << " ";++it;}cout << endl;*/for (auto e : object){cout << e << " ";}cout << endl;
}}

#include "vector.h"int main()
{ouyang::Vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);/*auto it = v1.begin();while (it != v1.end()){cout << *it << " ";++it;}cout << endl;ouyang::Vector<int> v2(v1);for (int i = 0; i < v2.size(); ++i){cout << v2[i] << " ";}cout << endl;*//*ouyang::Vector<int> v3(v1.begin(), v1.end());auto it = v3.begin();while (it != v3.end()){cout << *it << " ";++it;}cout << endl;*///ouyang::Vector<int> v4(5);//ouyang::Vector<int> v5(5, 1);//ouyang::Print(v4);//ouyang::Print(v5);//v5.clear();//ouyang::Print(v4);//ouyang::Print(v5);/*ouyang::Vector<int> v6;v6 = v1;ouyang::Print(v6);v6.insert(v6.begin(), 100);ouyang::Print(v6);v6.erase(v6.begin());ouyang::Print(v6);*/return 0;
}