一、构造函数

vector()   //构造函数
	:_start(nullptr)
	,_finish(nullptr)
	,_endofstorage(nullptr)
{}

vector(int n, const T& val = T())//构造函数
	:_start(nullptr)
	, _finish(nullptr)
	, _endofstorage(nullptr)
{
	reserve(n);
	while (n--)
	{
		push_back(val);
	}
}

template<class InputIterator>
vector(InputIterator first, InputIterator last)//构造函数
	:_start(nullptr)
	, _finish(nullptr)
	, _endofstorage(nullptr)
{
	while (first != last)
	{
		push_back(*first);
		first++;
	}
}

 二、拷贝构造

vector(const vector<T>& v)//拷贝构造
	:_start(nullptr)
	,_finish(nullptr)
	,_endofstorage(nullptr)
{
	reserve(v.capacity());
	for (auto& c : v)
	{
		push_back(c);
	}
}

三、析构

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

四、重载

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> tmp)
{
	swap(tmp);
	return *this;
}
T& operator[](size_t pos)
{
	assert(pos < size());
	return *(_start + pos);
}
const T& operator[](size_t pos) const
{
	assert(pos < size());
	return *(_start + pos);
}

五、扩容及增删

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

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

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

	insert(end(), val);
}

void reserve(size_t n)
{
	if (capacity() < n)
	{
		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;
	}
}

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 pop_back()
{
	_finish--;
}
void insert(iterator pos, const T& x)
{
	assert(pos >= _start);
	assert(pos <= _finish);
	if (_finish == _endofstorage)
	{
		size_t len = pos - _start;
		reserve(capacity() == 0 ? 4 : capacity() * 2);
		pos = _start + len;
	}
	
	iterator end = _finish - 1;
	while (end >= pos)
	{
		*(end + 1) = *end;
		end--;
	}
	*pos = x;
	_finish++;
}

void erase(iterator pos)
{
	assert(pos >= _start);
	assert(pos < _finish);
	while (pos != end())
	{
		*pos = *(pos + 1);
		pos++;
	}
	_finish--;
}

总体：

namespace asd //设一个命名空间避免与std冲突
{
	template<class T>
	class vector
	{
	public:
		typedef T* iterator;
		typedef const T* const_iterator;
		vector()   //构造函数
			:_start(nullptr)
			,_finish(nullptr)
			,_endofstorage(nullptr)
		{}

		vector(int n, const T& val = T())//构造函数
			:_start(nullptr)
			, _finish(nullptr)
			, _endofstorage(nullptr)
		{
			reserve(n);
			while (n--)
			{
				push_back(val);
			}
		}

		template<class InputIterator>
		vector(InputIterator first, InputIterator last)//构造函数
			:_start(nullptr)
			, _finish(nullptr)
			, _endofstorage(nullptr)
		{
			while (first != last)
			{
				push_back(*first);
				first++;
			}
		}

		vector(const vector<T>& v)//拷贝构造
			:_start(nullptr)
			,_finish(nullptr)
			,_endofstorage(nullptr)
		{
			reserve(v.capacity());
			for (auto& c : v)
			{
				push_back(c);
			}
		}

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

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

        //迭代器
		iterator begin()
		{
			return _start;
		}

		iterator end()
		{
			return _finish;
		}

		const_iterator cbegin() const
		{
			return _start;
		}

		const_iterator cend() const
		{
			return _finish;
		}

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

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

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

			insert(end(), val);
		}

		void reserve(size_t n)
		{
			if (capacity() < n)
			{
				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;
			}
		}

		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++;
				}
			}
		}

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

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

		void pop_back()
		{
			_finish--;
		}

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

		void insert(iterator pos, const T& x)
		{
			assert(pos >= _start);
			assert(pos <= _finish);
			if (_finish == _endofstorage)
			{
				size_t len = pos - _start;
				reserve(capacity() == 0 ? 4 : capacity() * 2);
				pos = _start + len;
			}
			
			iterator end = _finish - 1;
			while (end >= pos)
			{
				*(end + 1) = *end;
				end--;
			}
			*pos = x;
			_finish++;
		}

		void erase(iterator pos)
		{
			assert(pos >= _start);
			assert(pos < _finish);
			while (pos != end())
			{
				*pos = *(pos + 1);
				pos++;
			}
			_finish--;
		}
	private:
		iterator _start;
		iterator _finish;
		iterator _endofstorage;
	};
}