目录

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 

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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;
}