c++初阶--vector的实现

下面是vector的代码：

vector.h

#pragma once

#include
#include
using namespace std;

namespace one
{
	template
	class vector
	{
	public:
		typedef T* iterator;
		typedef const T* const_iterator;

		vector() = default;

		template
		vector(InputIterator first, InputIterator end)
		{
			while (first != end)
			{
				push_back(*first);
				first++;
			}
		}

		vector(size_t n, const T& x=T())
		{
			reserve(n);
			for (size_t i = 0; i < n; i++)
			{
				_head[i] = x;
				_rear++;
			}
		}

		vector(const vector& v)
		{
			reserve(v.capacity());
			for (const auto& e : v)
			{
				push_back(e);
			}
		}

		~vector()
		{
			if (_head)
			{
				delete[] _head;
				_head = _rear = _finish = nullptr;
			}
		}

		vector& operator=(vector v)
		{
			swap(v);
			return *this;
		}

		void reserve(size_t new_capacity)
		{
			if (new_capacity > capacity())
			{
				size_t old_size = size();
				T* tmp = new T[new_capacity];
				for (size_t i = 0; i < old_size; i++)
				{
					tmp[i] = _head[i];
				}
				delete[]_head;
				_head = tmp;
				_rear = _head + old_size;
				_finish = _head + new_capacity;
			}
		}

		void resize(size_t n, T x=T())
		{
			if (n > size())
			{
				if (n > capacity())
				{
					size_t old_size = size();
					T* tmp = new T[n];
					for (size_t i = 0; i < size(); i++)
					{
						tmp[i] = _head[i];
					}
					_head = tmp;
					_rear = _head + old_size;
					_finish = _head + n;
				}
				while (size() != capacity())
				{
					push_back(x);
				}
			}
			else {
				_rear = _head + n;
			}
		}

		size_t size()const
		{
			return _rear - _head;
		}

		size_t capacity()const
		{
			return _finish - _head;
		}

		size_t empty()const
		{
			return _head == _rear;
		}

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

		const T& operator[](size_t pos)const
		{
			assert(pos < size());
			return _head[pos];
		}

		void print_vector()
		{
			typename vector::iterator it = begin();
			while (it != end())
			{
				cout << *it << ' ';
				it++;
			}
			cout << endl;
		}

		iterator begin()
		{
			return _head;
		}

		iterator end()
		{
			return _rear;
		}

		const_iterator begin()const
		{
			return _head;
		}

		const_iterator end()const
		{
			return _rear; 
		}

		void push_back(const T& x)
		{
			if (_rear==_finish)
			{
				size_t new_capacity = capacity() == 0 ? 4 : (2 * capacity());
				reserve(new_capacity);
			}
			*_rear = x;
			_rear++;
		}

		void pop_back()
		{
			assert(!empty());
			_rear--;
		}

		iterator insert(iterator pos, const T& x)
		{
			assert(pos >= _head && pos <= _rear);
			if (_rear==_finish)
			{
				size_t tmp = pos - _head;
				size_t new_capacity = capacity() == 0 ? 4 : (2 * capacity());
				reserve(new_capacity);
				pos = _head + tmp;
			}
			typename vector::iterator it = end();
			_rear++;
			while (it != pos)
			{
				*(it + 1) = *it;
				it--;
			}
			*pos = x;
			return pos;
		}

		void erase(iterator pos)
		{
			assert(!empty());
			assert(pos >= _head && pos <= _rear);
			typename vector::iterator it = pos;
			while (it != end())
			{
				*it = *(it + 1);
				it++;
			}
			_rear--;
		}

		void swap(vector& v)
		{
			std::swap(_head, v._head);
			std::swap(_rear, v._rear);
			std::swap(_finish, v._finish);
		}
	private:
		T* _head = nullptr;
		T* _rear = nullptr;
		T* _finish = nullptr;
	};
}