模拟实现vector类

实现代码：vector.h

#pragma once
#include<assert.h>
#include<iostream>
using namespace std;

namespace bit
{
	template<class T>
	class vector
	{
	public:
		// Vector的迭代器是一个原生指针
		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() const
		{
			return _finish;
		}

		
		
		// construct and destroy
		vector()
		{}

		vector(size_t n, const T& value = T())
		{
			reserve(n);
			for (size_t i = 0; i < n; i++)
			{
				push_back(value);
			}
		}

		vector(int n, const T& value = T())
		{
			reserve(n);
			for (int i = 0; i < n; i++)
			{
				push_back(value);
			}
		}

		// 类模板的成员函数可以是函数模板
		template<class InputIterator>
		vector(InputIterator first, InputIterator last)
		{
			while (first != last)
			{
				push_back(*first);
				++first;
			}
		}

		//v2(v1)
		vector(const vector<T>& v)
		{
			reserve(v.capacity());
			for (auto& e : v)
			{
				push_back(e);
			}
		}

		// vector<int> v1 = { 1,2,3,4,5,6,7,8,9,10 };
		vector(initializer_list<T> il)
		{
			reserve(il.size());
			for (auto& e : il)
			{
				push_back(e);
			}
		}


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

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


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

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

		void reserve(size_t n)
		{
			if (n > capacity())
			{
				size_t old_size = size();
				T* tmp = new T[n];
				//memcpy(tmp, _start, size() * sizeof(T)); T是string,调用memcpy的话，string就是浅拷贝了
				for (size_t i=0;i<old_size;i++)
				{
					tmp[i] = _start[i];
				}
				delete[] _start;

				_start = tmp;
				_finish = tmp + old_size;
				_endofstorage = tmp + n;
			}
		}

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

		///access///

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

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

			return _start[pos];
		}


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

		void push_back(const T& val)
		{
			if (_finish == _endofstorage)
			{
				reserve(capacity() == 0 ? 4 : capacity() * 2);
			}
			*_finish = val;
			++_finish;
		}

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

		bool empty()
		{
			return _start == _finish;
		}

		iterator insert(iterator pos, const T& val)
		{
			assert(pos <= _finish && pos >= _start);

			if (_finish == _endofstorage)
			{
				size_t len = pos - _start;
				reserve(capacity() == 0 ? 4 : capacity() * 2);

				// 如果扩容了要更新pos
				pos = _start + len;
			}

			it