vector 使用：

1.vector的构造函数：

2.vector iterator 的使用：

3.vector 容量操作：

4.vector 增删查改：

vector 模拟实现：

#pragma once

#include <assert.h>

namespace yx
{
	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()
		{
			return _finish;
		}

		//vector(size_t n, const T& val = 0);如果T为int这样可以，但是T的类型不确定，
		//故只能调用匿名构造函数,当然已对其进行优化可以处理内置类型,int i = 0;int i = int();int i = int(1);
		vector(size_t n, const T& val = T())
		{
			resize(n, val);
		}

		vector(int n, const T& val = T())
		{
			resize(n, val);
		}

		template<class InputIterator>
		vector(InputIterator first, InputIterator last)
		{
			while (first != last)
			{
				push_back(*first);
				++first;
			}
		}

		vector()
		{ }

		vector(const vector<T>& v)
		{
			_start = new T[v.capacity()];
			//memcpy(_start, v._start, sizeof(T)*v.size());此处是浅拷贝，vector应是深拷贝
			for (size_t i = 0; i < v.size(); i++)
			{
				_star[i] = v._start[i];
			}

			_finish = _start + v.size();
			_endofstorage = _start + v.capacity();//_endofstorage = v._endofstorage;_endofstorage不是数字而是指针
		}

		void swap(vector<T>& v)
		{
			std::swap(_start, v._start);
			std::swap(_finish, v._finish);
			std::swap(_endofstorage, v._endofstorage);
		}

		vector<T>& operator=(vector<T> v)
		{
			swap(v);

			return *this;
		}

		//vector<T>& operator=(const vector<T>& v)
		//{
		//	if (this != &v)
		//	{
		//		T* tmp = new T[v.capacity()];
		//		//void * memcpy ( void * destination, const void * source, size_t num );
		//		//memcpy(tmp, v.begin(), sizeof(T) * v.size());
		//		for (size_t i = 0; i < v.size(); i++)
		//		{
		//			tmp[i] = v[i];
		//		}
		//		delete[] _start;
		//		_start = tmp;

		//		_finish = _start + v.size();
		//		_endofstorage = _start + v.capacity();
		//	}

		//	return *this;
		//}

		~vector()
		{
			if (_start)
			{
				delete[] _start;
				_start = _finish = _endofstorage = nullptr;
			}
		}

		void reserve(size_t n)
		{
			if (n > capacity)
			{
				szie_t sz = size();
				T* tmp = new T[n];
				if (_start)
				{
					for (size_t i = 0; i < sz; i++)
					{
						tmp[i] = _start[i];
					}
					delete[] _start;
				}
				_start = tmp;
				_finish = _start + sz;
				//_finish = _start + size();此处_start已指向新空间，而_finish还未更新，所以时错的
				_endofstorage = _start + n;
			}
		}

		void resize(size_t n, const T& val = T())
		{
			if (n < size())
			{
				_finish = _start + n;
			}
			else
			{
				reserve(n);

				while (_finish != _start + n)
				{
					*_finish = val;
					++_finish;
				}
			}
		}

		void push_back(const T& x)
		{
			/*if (_finish == _endofstorage)
			{
				size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newcapacity);
			}

			*_finish = x;
			++_finish;*/
			insert(end(), x);
		}

		void pop_back()
		{
			erase(--end());
		}

		size_t size()const
		{
			return _finish - _start;
		}

		size_t capacity()const
		{
			return _endofstorage - _start;
		}

		T& operator[](size_t pos)
		{
			assert(pos < size());

			return _start[pos];
		}

		iterator insert(iterator pos, const T& x)
		{
			assert(pos >= _start && pos <= _finish)
			
			if (_finish == _endstorage)
			{
				size_t len = pos - _start;//保存pos的相对位置，防止扩容导致迭代器失效

				size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newcapacity);

				pos = _start + len;//解决迭代器失效问题，但在外部仍存在
			}

			iterator end = _finish - 1;
			while (end >= pos)
			{
				*(end + 1) = *end;
				--end;
			}

			*pos = x;
			++_finish;

			return pos;
		}//insert以后迭代器可能会失效(扩容)，insert以后不要使用这个形参迭代器了，应为他可能失效了

		iterator erase(iterator pos)
		{
			assert(pos >= _start && pos < _finish);

			iterator it = pos + 1;
			while (it != _finish)
			{
				*(it - 1) = *it;
				++it;
			}
			--_finish;
			return pos;
		}//erase结束后也不可访问迭代器，vs强制检查访问会直接报错,所以在insert和erase后不要访问

	private:
		iterator _start = nullptr;
		iterator _finish = nullptr;
		iterator _endofstorage = nullptr;
	};
}