一、vector的使用

1.1 vector的定义

本质讲，vector使用动态分配数组来存储它的元素

string、vector等都有一个特点，删除数据，一般是不会主动缩容

int main()
{
	//v1 12345
	vector<int> v1;
	v1.push_back(1);
	v1.push_back(2);
	v1.push_back(3);
	v1.push_back(4);
	v1.push_back(5);
 
	//v2   1.1,2.2,3.3,4.4,5.5
	vector<double> v2;
	v2.push_back(1.1);
	v2.push_back(2.2);
	v2.push_back(3.3);
	v2.push_back(4.4);
	v2.push_back(5.5);
 
	//v3 克里斯蒂亚诺里昂内尔内马尔
	vector v3;
	v3.push_back("克里斯蒂亚诺");
	v3.push_back("里昂内尔");
	v3.push_back("内马尔");
 
 
	//v4构造并初始化10个5
	vector<int> v4(10, 5);
 
	//v5 里斯蒂亚诺里昂内尔内马
	vector v5(++v3.begin(), --v3.end());
 
	string s = "hello world";
 
	//v6 "hello world"
	vector<char> v6(s.begin(), s.end());
 
	return 0;
}

1.2 vector iterator的使用

int main()
{
	vector<int> v1;
	v1.push_back(1);
	v1.push_back(2);
	v1.push_back(3);
	v1.push_back(4);
	v1.push_back(5);
 
	//遍历
	//1.下标+[]
	for (size_t i = 0; i < v1.size(); i++)
	{
		cout << v1[i] << " ";
	}
	cout << endl;
 
	//2.迭代器
	vector<int> ::iterator it = v1.begin();
	while (it != v1.end())
	{
		cout << *it << " ";
		it++;
	}
	cout << endl;
 
	//3.范围for
	for (auto c : v1)
	{
		cout << c << " ";
	}
	cout << endl;
 
	return 0;
}

1.3 vector 迭代器失效问题 

vector迭代器失效有两种：

1. 扩容、缩容，导致野指针式失效。
2. 迭代器指向的意义变了

vector检查迭代器失效的两种机制：

1. 系统越界机制检查（不一定能检查到）
2. 编译实现机制检查（相对靠谱）

对于insert和erase造成的迭代器失效问题，linux（g++）平台检查很佛系，基本依靠操作系统野指针越界检查机制；windows下VS系列检查更严格，使用一些强制检查机制，意义变了也可能会检查出来。

1.4 vector构建二维动态数组

 

vector构建动态二维数组时与上图实际是一致的 

---

二、vector的模拟实现

namespace Cris
{
	template <class T>
	class vector
	{
	public:
		typedef T* iterator;
		typedef const T* const_iterator;
 
		vector()
			:_start(nullptr)
			, _finish(nullptr)
			, _endofstoage(nullptr)
		{}
 
		template <class InputIterator>
		vector(InputIterator first, InputIterator last)
			: _start(nullptr)
			, _finish(nullptr)
			, _endofstoage(nullptr)
		{
			while (first != last)
			{
				push_back(*first);
				++first;
			}
		}
 
		vector(size_t n, const T& val = T())
			: _start(nullptr)
			, _finish(nullptr)
			, _endofstoage(nullptr)
		{
			reserve(n);
			for (size_t i = 0; i < n; ++i)
			{
				push_back(val);
			}
		}
 
		vector(int n, const T& val = T())
			: _start(nullptr)
			, _finish(nullptr)
			, _endofstoage(nullptr)
		{
			reserve(n);
			for (int i = 0; i < n; ++i)
			{
				push_back(val);
			}
		}
 
		void swap(vector& v)
		{
			std::swap(_start, v._start);
			std::swap(_finish, v._finish);
			std::swap(_endofstoage, v._endofstoage);
		}
 
		vector(const vector& v)
			: _start(nullptr)
			, _finish(nullptr)
			, _endofstoage(nullptr)
		{
			vector tmp(v.begin(), v.end());
			swap(tmp);
		}
 
		vector& operator=(vector v)
		{
			swap(v);
			return *this;
		}
 
 
 
		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 _endofstoage - _start;
		}
 
		void reserve(size_t n)
		{
			size_t sz = size();
			if (n > capacity)
			{
				T* tmp = new T[n];
				if (_start)
				{
					//扩容使用memcpy拷贝数据是存在浅拷贝问题
					//memcpy(tmp, _start, size() * sizeof(T));
					//解决方法：
					for (size_t i = 0; i < size(); i++)
					{
						tmp[i] = _start[i];
					}
					delete[] _start;
				}
 
				_start = tmp;
			}
 
			_finish = _start + sz;
			_endofstoage = _start + n;
		}
 
		//T() ---- T的构造函数
		//void resize(size_t n,const T& val = T())
		void resize(size_t n, T val = T())
		{
			if (n > capacity())
			{
				reserve(n);
			}
 
			if (n > size())
			{
				while (_finish < _start + n)
				{
					*_finish = val;
					++_finish;
				}
			}
			else
			{
				_finish = _start + n;
			}
		}
 
		void push_back(const T& x)
		{
			/*if (_finish == _endofstoage)
			{
				size_t newCapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newCapacity);
			}
			*_finish = x;
			++_finish;*/
 
			insert(end(), x);
		}
 
		void pop_back()
		{
			if (_finish < _start)
			{
				--_finish;
			}
		}
 
		T& operator[](size_t pos)
		{
			assert(pos < size());
 
			return _start[pos];
		}
 
		const T& operator[](size_t pos) const
		{
			assert(pos < size());
 
			return _start[pos];
		}
 
		iterator insert(iterator pos, const T& x)
		{
			// 检查参数
			assert(pos >= _start && pos <= _finish);
 
			// 扩容
			// 扩容以后pos就失效了,需要更新一下
			if (_finish == _endofstoage)
			{
				size_t n = pos - _start;
 
				size_t newCapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newCapacity);
 
				pos = _start + n;
			}
 
			// 挪动数据
			iterator end = _finish - 1;
			while (end >= pos)
			{
				*(end + 1) = *end;
				--end;
			}
 
			*pos = x;
			++_finish;
 
			return pos;
		}
 
		iterator erase(iterator pos)
		{
			assert(pos >= _start && pos < _finish);
			iterator it = pos + 1;
			while (it != _finish)
			{
				*(it - 1) = *it;
				++it;
			}
 
			--_finish;
 
			return pos;
		}
 
		void clear()
		{
			_finish = _start;
		}
 
	private:
		iterator _start;
		iterator _finish;
		iterator _endofstoage;
	};
}

 

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