C++ 中的 vector 的模拟实现【代码纯享】

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文章目录

C++ 中的 vector 模拟实现
- 1. vector 的基本概念
- 2. vector 的基本操作
- 3. vector 的模拟实现
- 4.代码纯享
- 5. 总结

C++ 中的 vector 模拟实现

在 C++ 中，vector 是一个非常重要的容器，它提供了动态数组的功能。在本篇博客中，我们将尝试模拟实现一个简单的 vector 类，以便更好地理解其内部工作机制。

1. vector 的基本概念

vector 是一个封装了动态大小数组的顺序容器。与普通数组不同，vector 的大小可以根据需要动态地增加或减少，而不需要程序员手动管理内存。

2. vector 的基本操作

构造函数：创建一个空的 vector 或者根据给定的初始值创建一个 vector。
赋值操作：将一个 vector 的内容赋值给另一个 vector。
访问元素：通过索引访问 vector 中的元素。
插入和删除元素：在 vector 的任何位置插入或删除元素。
大小操作：获取 vector 的大小或检查它是否为空。
迭代器操作：提供迭代器以遍历 vector 中的元素。

3. vector 的模拟实现

首先，我们需要定义vector的基本结构。由于vector可以存储不同类型的元素，我们使用类模板来定义它：

namespace my_vector
{template<class T>class vector{public:// 定义迭代器类型typedef T* iterator;// 定义const迭代器类型typedef const T* const_iterator;// 其他成员变量和成员函数...
};

接下来，我们实现vector的一些基本成员函数，如默认构造函数，析构函数，拷贝构造函数：

		iterator begin(){return _start;}iterator end(){return _finish;}const_iterator begin() const{return _start;}const_iterator end() const{return _finish;}vector(){}//拷贝构造v2(v1)vector(const vector<T>& v){reserve(v.capacity());for (auto& e : v){push_back(e);}}//vector<int> v1 = { 1, 2, 3, 4, 5, 6, 7, 8 };//构造+拷贝构造 -> 优化 直接构造vector(initializer_list<T> il){reserve(il.size());for (auto& e : il){push_back(e);}}vector(size_t n, const T& val = T()){reserve(n);for (size_t 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);}}//深拷贝 v1=v3vector<T>& operator=(vector<T> v){swap(v);return *this;}~vector(){delete[] _start;_start = _finish = _endofstorage = nullptr;}
private:iterator _start = nullptr;iterator _finish = nullptr;iterator _endofstorage = nullptr;

然后，我们实现vector的迭代器。迭代器是一种行为类似于指针的对象，它能够遍历容器中的元素：

		bool empty(){return _start == _finish;}void insert(iterator pos, const T& val){assert(pos >= _start);assert(pos <= _finish);if (_finish == _endofstorage){size_t len = pos - _start;reserve(capacity() == 0 ? 4 : capacity() * 2);//如果扩容了要更新pospos = _start + len;}iterator it = _finish - 1;while (it >= pos){*(it + 1) = *it;it--;}*pos = val;_finish++;}iterator erase(iterator pos){assert(pos >= _start);assert(pos < _finish);iterator it = pos + 1;while (it < _finish){*(it - 1) = *it;it++;}--_finish;return pos;}

最后，我们实现vector的一些基本操作，如push_back、pop_back、begin、end等：

size_t size() const{return _finish - _start;}T& operator[](size_t pos){assert(pos < size());return _start[pos];}const T& operator[](size_t pos) const{assert(pos < size());return _start[pos];}size_t capacity() const {return _endofstorage - _start;}void reserve(size_t n){if (n > capacity()){T* tmp = new T[n];size_t old_size = size();//memcpy(tmp, _start, size()*sizeof(T));for (size_t i = 0; i < old_size; i++){tmp[i] = _start[i];}delete[] _start;_start = tmp;_finish = tmp + old_size;_endofstorage = tmp + n;}}void resize(size_t n,const T& val=T()){if (n > size()){reserve(n);//插入while (_finish<_start + n){*_finish = val;_finish++;}}else{//删除_finish = _start + n;}}void push_back(const T& val){/*if (_finish == _endofstorage){reserve(capacity() == 0 ? 4 : capacity() * 2);}*_finsh = val;_finsh++;*/insert(end(), val);}void pop_back(){/*assert(empty());_finsh--;*/erase(--end());}

4.代码纯享

#pragma once
#include <assert.h>namespace my_vector
{template<class T>class vector{public:// 定义迭代器类型typedef T* iterator;// 定义const迭代器类型typedef const T* const_iterator;// 其他成员变量和成员函数...iterator begin(){return _start;}iterator end(){return _finish;}const_iterator begin() const{return _start;}const_iterator end() const{return _finish;}vector(){}//拷贝构造v2(v1)vector(const vector<T>& v){reserve(v.capacity());for (auto& e : v){push_back(e);}}//vector<int> v1 = { 1, 2, 3, 4, 5, 6, 7, 8 };//构造+拷贝构造 -> 优化 直接构造vector(initializer_list<T> il){reserve(il.size());for (auto& e : il){push_back(e);}}//类模板的成员函数可以是函数模板template <class InputIerator>vector(InputIerator first, InputIerator last){while (first != last){push_back(*first);first++;}}vector(size_t n, const T& val = T()){reserve(n);for (size_t 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);}}void swap(vector<T>& v){std::swap(_start, v._start);std::swap(_finsh, v._finsh);std::swap(_endofstorage, v._endofstorage);}//深拷贝 v1=v3vector<T>& operator=(vector<T> v){swap(v);return *this;}~vector(){delete[] _start;_start = _finish = _endofstorage = nullptr;}size_t size() const{return _finish - _start;}T& operator[](size_t pos){assert(pos < size());return _start[pos];}const T& operator[](size_t pos) const{assert(pos < size());return _start[pos];}size_t capacity() const {return _endofstorage - _start;}void reserve(size_t n){if (n > capacity()){T* tmp = new T[n];size_t old_size = size();//memcpy(tmp, _start, size()*sizeof(T));for (size_t i = 0; i < old_size; i++){tmp[i] = _start[i];}delete[] _start;_start = tmp;_finish = tmp + old_size;_endofstorage = tmp + n;}}void resize(size_t n,const T& val=T()){if (n > size()){reserve(n);//插入while (_finish<_start + n){*_finish = val;_finish++;}}else{//删除_finish = _start + n;}}void push_back(const T& val){/*if (_finish == _endofstorage){reserve(capacity() == 0 ? 4 : capacity() * 2);}*_finsh = val;_finsh++;*/insert(end(), val);}void pop_back(){/*assert(empty());_finsh--;*/erase(--end());}bool empty(){return _start == _finish;}void insert(iterator pos, const T& val){assert(pos >= _start);assert(pos <= _finish);if (_finish == _endofstorage){size_t len = pos - _start;reserve(capacity() == 0 ? 4 : capacity() * 2);//如果扩容了要更新pospos = _start + len;}iterator it = _finish - 1;while (it >= pos){*(it + 1) = *it;it--;}*pos = val;_finish++;}iterator erase(iterator pos){assert(pos >= _start);assert(pos < _finish);iterator it = pos + 1;while (it < _finish){*(it - 1) = *it;it++;}--_finish;return pos;}private:iterator _start = nullptr;iterator _finish = nullptr;iterator _endofstorage = nullptr;};//函数模板//template <typename T>template <class T>void print_vector(const vector<T>& v){for (size_t i = 0; i < v.size(); i++){cout << v[i] << " ";}cout << endl;//typename vector<int>::const_iterator it = v.begin();//	auto it = v.begin();//	while (it != v.end())//	{//		cout << *it << " ";//		it++;//	}//	cout << endl;//	for (auto e : v)//	{//		cout << e << " ";//	}//	cout << endl;}void test_vector1(){vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);v1.push_back(6);print_vector(v1);v1.insert(v1.begin(),3);v1.insert(v1.begin() + 2, 3);v1.insert(v1.begin() + 4, 3);v1.insert(v1.begin() + 6, 3);print_vector(v1);v1.erase(v1.begin()+4);print_vector(v1);vector<double> v2;v2.push_back(0.1);v2.push_back(0.2);v2.push_back(0.3);v2.push_back(0.4);v2.push_back(0.5);v2.push_back(0.6);print_vector(v2);}void test_vector2(){vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);v1.push_back(6);print_vector(v1);v1.resize(10);print_vector(v1);v1.resize(3);print_vector(v1);}void test_vector3(){vector<int> v3(10,1);print_vector(v3);}void test_vector4(){auto x = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };cout << typeid(x).name() << endl;cout << sizeof(x) << endl;initializer_list<int> y = { 1, 2, 3, 4, 5, 6, 7 };//单参数的构造函数，隐式类型转换string str = "111111";//构造+拷贝构造->优化 直接构造const string& str1 = "111111";//构造+拷贝构造->优化 直接构造vector<string> v;v.push_back(str);v.push_back(string("22222"));v.push_back("33333");int i = 1;//不推荐 --- C++11int j = { 1 };int k{ 1 };//跟上面类似//隐式转化+优化vector<int> v1 = { 1, 2, 3, 4, 5, 6, 7, 8 };for (auto e : v1){cout << e << " ";}cout << endl;//直接构造vector<int> v2({ 1, 2, 3, 10, 20, 30 });for (auto e : v2){cout << e << " ";}cout << endl;}void test_vector5(){vector<string> v;v.push_back("11111");v.push_back("11111");v.push_back("11111");v.push_back("11111");v.push_back("11111");v.push_back("11111");for (auto& e : v){cout << e << " ";}cout << endl;}void test_vector6(){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);print_vector(v1);vector<int>::iterator it = v1.begin() + 3;v1.insert(it, 40);print_vector(v1);}
}