模拟实现vector:vector构造、析构函数、size、capacity、push_back函数、迭代器、[]运算符重载等的介绍

文章目录

前言
一、vecotr构造、析构函数、size、capacity、push_back函数、迭代器、[]运算符重载
二、insert函数
三、const修饰的迭代器
总结

前言

模拟实现vector:vector构造、析构函数、size、capacity、push_back函数、迭代器、[]运算符重载等的介绍

一、vecotr构造、析构函数、size、capacity、push_back函数、迭代器、[]运算符重载

参考vector的源代码，vector的成员变量的结构:

private：iterator _start;iterator _finish;iterator _end_of_storage;

iterator为模板指针类型，通过typedef重命名。

vector的结构大致为如下:

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#include <iostream>
#include <assert.h>using namespace std;namespace hhb
{template <class T>class vector{public:typedef T* iterator;typedef const T* const_iterator;iterator begin() {return _start;}iterator end() {return _finish;}const_iterator begin() const{return _start;}const_iterator end() const{return _finish;}vector(): _start(nullptr), _finish(nullptr), _end_of_storage(nullptr){}~vector(){delete[] _start;_start = _finish = _end_of_storage = nullptr;}void push_back(const T& x){size_t newcapacity = capacity() == 0 ? 4 : 2 * capacity();if (_finish == _end_of_storage){reserve(newcapacity);}*_finish = x;++_finish;}//void reserve(size_t n)//{//	if (n > capacity())//	{//		T* tmp = new T[n];//		memcpy(tmp, _start, sizeof(T) * size());//		delete[] _start;//		_finish = tmp + size();//		_start = tmp;//		_end_of_storage = _start + n;//	}//	//}void reserve(size_t n){if (n > capacity()){size_t sz = size();T* tmp = new T[n];memcpy(tmp, _start, sizeof(T) * sz);delete[] _start;_start = tmp;_finish = _start + sz;_end_of_storage = _start + n;}}size_t capacity() const{return _end_of_storage - _start;}size_t size() const{return _finish - _start;}private:iterator _start;iterator _finish;iterator _end_of_storage;};
}

resereve的经典小坑：

void reserve(size_t n)
{if (n > capacity()){T* tmp = new T[n];memcpy(tmp, _start, sizeof(T) * size());delete[] _start;_start = tmp;_finish = _start + size();_end_of_storage = _start + n;}
}

如上述的写法：
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测试执行

#include "vector.h"void Test_vector1()
{hhb::vector<int> v1;v1.push_back(1);v1.push_back(2);v1.push_back(3);v1.push_back(4);v1.push_back(5);for (size_t i = 0; i < v1.size(); i++){cout << v1[i] << " ";}cout << endl;hhb::vector<int>::iterator it = v1.begin();while (it != v1.end()){cout << *it << " ";++it;}cout << endl;for (auto e : v1){e++;cout << e << " ";}cout << endl;
}int main()
{Test_vector1();//Test_vector2();//Test_vector3();return 0;
}

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二、insert函数

iterator insert(iterator pos, const T& x)
{assert(pos >= _start && pos <= _finish);if (_finish == _end_of_storage){size_t len = pos - _start;size_t newcapacity = capacity() == 0 ? 4 : 2 * capacity();reserve(newcapacity);pos = _start + len;}iterator end = _finish - 1;while (end >= pos){*(end + 1) = *end;--end;}*pos = x;++_finish;return _start;
}

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这里会有一个迭代器失效的坑

三、const修饰的迭代器

void print(const hhb::vector<int>& v)
{for (auto e : v){cout << e << " ";}cout << endl;
}
void Test_vector3()
{hhb::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);v1.push_back(7);v1.push_back(8);print(v1);
}