C++ vector(2)

vector 模拟实现

#pragma once
#include <iostream>
using namespace std;
#include <assert.h>
namespace bit
{
	template<class T>
	class vector
	{
	public:
		typedef   const T*  const_iterator;
		typedef T* iterator;
		iterator begin()
		{
			return _start;
		}
		iterator end()
		{
			return _finish;
		}
			const_iterator begin() const
		{
			return _start;
		}
			const_iterator end() const
			{
				return _finish;
			}
			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()
			{
				if (_start)
				{
					delete[] _start;
					_start = _finish = _endofstorage = nullptr;
				}
			}
			vector()
			{
			}
		void push_back(const T& x)
		{
			insert(end(), x);
         }
			size_t capacity()  const
		{
			return _endofstorage - _start;
		}
		size_t size()  const
		{
			return _finish - _start;
		}
		void reserve(size_t n)
		{
			if (n > capacity())
			{
				size_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;
				_endofstorage = _start + n;
			}
		}
		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)
		{
			assert(pos >= _start && pos <= _finish);
			if (_finish == _endofstorage)
			{
				size_t len = pos - _start;
				size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newcapacity);
				pos = _start + len;
			}
			iterator end = _finish - 1;
			while (end >= pos)
			{
				*(end + 1) = *end;
				--end;
			}
			*pos = x;
			++_finish;
			return pos;
		}
		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;
				}
			}
		}
		vector(const vector<T>& v)
		{
			_start = new T[v.capacity()];
			for (size_t i = 0; i < v.size(); i++)
			{
				_start[i] = v._start[i];
			}
			_finish = _start + v.size();
			_endofstorage = _start + v.capacity();
		}
		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;
		}
		iterator erase(iterator pos)
		{
			assert(pos >= _start && pos < _finish);
			iterator it = pos + 1;
			while (it != _finish)
			{
				*(it - 1) = *it;
				++it;
			}
			--_finish;
			return pos;
		}
		void pop_back()
		{
			erase(--end());
		}
	private:
		iterator _start = nullptr;
		iterator _finish = nullptr;
		iterator _endofstorage = nullptr;
	};
	void print(vector<int>&v1)
	{
		for (auto e : v1)
		{
			cout << e << " ";
		}
	}
	void test_vector1()
	{
		vector <int> v1;
		v1.push_back(3);
		v1.push_back(2);
		v1.push_back(5);
		v1.push_back(56);
		v1.push_back(57);
		print(v1);
	}
}