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C++初阶——简单实现vector

news 2025/8/8 22:04:54

1、前言

2、Vector.h

3、Test.cpp

1、前言

简单实现std::vector类模板。

相较于前面的string，vector要注意：

深拷贝，因为vector的元素可能是类类型，类类型元素可以通过赋值重载，自己实现深拷贝。

迭代器失效，其实无非是两种(现在认为)：

1. 迭代器更新了，但是认为用的是之前的迭代器，可以先保存值。

2. 迭代器没有更新，但是认为是用更新后的迭代器，那就更新迭代器。

2、Vector.h

#pragma once#include <iostream>
#include <vector>
#include <assert.h>using namespace std;namespace Lzc
{template <class T>class vector{public:typedef T* iterator;typedef const T* const_iterator;vector() // 有了拷贝构造，就不会生成默认构造，但是需要默认构造{}vector(size_t n, const T& val = T())// int有默认构造int(),为了兼容模板{reserve(n);for (size_t i = 0; i < n; i++){push_back(val);}}template <class InputIterator> // 使用别的容器的迭代器初始化vector(InputIterator first, InputIterator last){// reserve(last - first);// last - first 有迭代器不支持减while (first != last){push_back(*first);++first;}}vector(const vector<T>& v){reserve(v.size());for (int i = 0; i < v.size(); i++){push_back(v[i]);}}void swap(vector<T>& tmp){std::swap(_start, tmp._start);std::swap(_finish, tmp._finish);std::swap(_end_of_storage, tmp._end_of_storage);}vector<T>& operator=(const vector<T>& v){vector tmp(v);swap(tmp);return *this;}~vector(){if (_start){delete[] _start;_start = _finish = _end_of_storage = nullptr;}}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;}void clear(){_finish = _start;}bool empty() 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];}void resize(size_t n, const T& val = T()); // resize一般用于扩容+初始化void reserve(size_t n);void push_back(const T& val){if (size() == capacity())reserve(capacity() == 0 ? 4 : 2 * capacity());*_finish = val;++_finish;}void pop_back(){assert(size() > 0);--_finish;}iterator insert(iterator pos, const T& val);iterator erase(iterator pos);private:iterator _start = nullptr;iterator _finish = nullptr;iterator _end_of_storage = nullptr;};template<class T>void vector<T>::resize(size_t n, const T& val) // resize一般用于扩容+初始化{if (n < size()){_finish = _start + n;}else{reserve(n);while (_finish < _start + n){*_finish = val;++_finish;}}}template<class T>void vector<T>::reserve(size_t n){if (n > capacity()){size_t old_size = size();T* tmp = new T[n];for (size_t i = 0; i < old_size; i++){tmp[i] = _start[i]; // 若为类类型，会赋值重载，先释放，再深拷贝}delete[] _start;_start = tmp;_finish = tmp + old_size; // 不能调用size(),因为_start已更新，所以先保存size()_end_of_storage = tmp + n;}}// vector<T>::iterator编译器认为是类中的静态变量，typename告诉编译器是类型template<class T>typename vector<T>::iterator vector<T>::insert(iterator pos, const T& val){assert(pos <= _finish);assert(pos >= _start);if (size() == capacity()){size_t old_pos = pos - _start; // 扩容后pos没有指向新空间reserve(capacity() == 0 ? 4 : 2 * capacity());pos = _start + old_pos;}iterator it = _finish;while (it != pos){*it = *(it - 1); // 若为类类型，会赋值重载，先释放，再深拷贝--it;}*pos = val;++_finish;return pos;}template<class T>typename vector<T>::iterator vector<T>::erase(iterator pos){assert(pos >= _start);assert(pos < _finish);iterator it = pos + 1;while (it != end()){*(it - 1) = *it; // 若为类类型，会赋值重载，先释放，再深拷贝++it;}--_finish;return pos;}template<class Container> // 什么容器都能打印void print_Container(const Container& v){for (const auto& e : v){cout << e << " ";}cout << endl;}
}

3、Test.cpp

#include "Vector.h"
#include <list>
#include <string>namespace Lzc
{void test_vector1(){vector<int> v;v.push_back(1);v.push_back(2);v.push_back(3);v.push_back(4);v.push_back(5);for (size_t i = 0; i < v.size(); i++){cout << v[i] << " ";}cout << endl;//vector<int>::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;vector<double> vd;vd.push_back(1.1);vd.push_back(1.2);vd.push_back(1.3);vd.push_back(1.4);vd.push_back(1.5);print_Container(vd);}void test_vector2(){vector<int> v;v.push_back(1);v.push_back(2);v.push_back(3);v.push_back(4);v.push_back(5);print_Container(v);// 若iterator insert(iterator& pos, const T& val)// 下面的临时变量(具有常性)，不能传引用/*v.insert(v.begin() + 2, 30);print_vector(v);*/int x;cin >> x;auto p = find(v.begin(), v.end(), x);if (p != v.end()){// insert以后p就是失效，不要直接访问，要访问就要更新这个失效的迭代器的值/*v.insert(p, 20);(*p) *= 10;*/p = v.insert(p, 40);(*(p + 1)) *= 10;}print_Container(v);}void test_vector3(){vector<int> v;v.push_back(1);v.push_back(2);v.push_back(3);v.push_back(4);//v.push_back(5);print_Container(v);// 删除所有的偶数auto it = v.begin();while (it != v.end()){if (*it % 2 == 0){it = v.erase(it); // 删除了，相当于++了}else{++it;}}print_Container(v);}void test_vector4(){int i = int(); // int有默认构造int(),为了兼容模板int j = int(1);int k(2);vector<int> v;v.resize(10, 1);v.reserve(20);print_Container(v);cout << v.size() << endl;cout << v.capacity() << endl;v.resize(15, 2);print_Container(v);v.resize(25, 3);print_Container(v);v.resize(5);print_Container(v);}void test_vector5(){vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);print_Container(v1);vector<int> v2 = v1;print_Container(v2);vector<int> v3;v3.push_back(10);v3.push_back(20);v3.push_back(30);v1 = v3;print_Container(v1);print_Container(v3);}void test_vector6(){vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(4);v1.push_back(4);vector<int> v2(v1.begin(), v1.begin() + 3);print_Container(v1);print_Container(v2); // 1 2 3list<int> lt;lt.push_back(10);lt.push_back(10);lt.push_back(10);lt.push_back(10);vector<int> v3(lt.begin(), lt.end()); print_Container(lt);print_Container(v3);// 10 10 10 10vector<string> v4(10, "1111111");print_Container(v4);vector<int> v5(10);print_Container(v5);vector<int> v6(10u, 1); // 指定构造函数，不然编译器会使用模板函数。print_Container(v6);    // vector(size_t n, const T& val = T())//vector<int> v7(10, 1); // 编译器会使用模板函数，报错//print_Container(v7); // 可以再重载一个vector(int n, const T& val = T())}void test_vector7() // 扩容后需深拷贝{vector<string> v;v.push_back("11111111111111111111");v.push_back("11111111111111111111");v.push_back("11111111111111111111");v.push_back("11111111111111111111");print_Container(v);v.push_back("11111111111111111111");print_Container(v);}
}int main()
{Lzc::test_vector7();return 0;
}

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