vector的简单实现

vector的成员变量其实是由一些列指针构造，他们分别是起始位置的_start，和数据段终止位置的_finish,空间容量终止位置的_endofstorage构成。

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

namespace Solution
{
	template<class T>
	class vector
	{
	public:
		typedef T* iterator;
		typedef const T* const_iterator;
		vector()
			:_start(nullptr)
			,_finish(nullptr)
			,_endofstorage(nullptr)
		{}
		//实现拷贝构造，先开一样的空间,再拷贝
		vector(const vector<T>& v)
			:_start(nullptr)
			,_finish(nullptr)
			,_endofstorage(nullptr)
		{
			reserve(v.capacity());
			//因为memcpy是浅拷贝，故不考虑,用深拷贝赋值拷贝
			if (_start)
			{
				for (size_t i = 0; i < v.size(); ++i)
				{
					*(_start + i) = *(v._start + i);
				}
			}
			_finish = _start + v.size();
			_endofstorage = _start + v.capacity();
		}
		~vector()
		{
			delete[] _start;
			_start = _finish = _endofstorage = nullptr;
		}
		//尾插
		void push_back(const T& val)
		{
			if (_finish == _endofstorage)
			{
				size_t capacity1 = capacity();
				size_t newcapacity = capacity1 == 0 ? 4 : 2 * capacity1;
				reserve(newcapacity);
			}//实现扩容
			*_finish = val;
			++_finish;
			//插入数据
		}

		//尾删
		void pop_back()
		{
			assert(_start != _finish);
			_finish--;
		}
		//插入
		void insert(iterator pos, const T& val)
		{
			assert(pos >= _start && pos <= _finish);
			if (_finish == _endofstorage)
			{
				size_t capacity1 = capacity();
				size_t newcapacity = capacity1 == 0 ? 4 : 2 * capacity1;
				reserve(newcapacity);
			}//扩容

			iterator end1 = end() - 1;
			while (end1 >= pos)
			{
				*(end1+1) = *end1;
				--end1;
			}
			*pos = val;
			_finish++;
		}

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

		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 reserve(size_t n)
		{
			if (n > capacity())
			{
				size_t sz = size();
				T* tmp = new T[n];

				//memcpy(tmp, _start, sz);//思考是否有问题
				for (size_t i = 0; i < sz; ++i)
				{
					*(tmp + i) = *(_start + i);
				}

				delete[] _start;
				_start = tmp;
				_finish = tmp + sz;
				_endofstorage = tmp + n;
			}
		}

		//-----------------
		iterator begin()const
		{
			return _start;
		}
		
		iterator end()const
		{
			return _finish;
		}
		//--------------------

		T& operator[](size_t n)
		{
			assert(n < size());
			return *(_start + n);
		}
		
		vector<T>& operator=(const vector<T>& v)  // 将一个数据拷贝到另一个数据中
		{
			if (this != &v)
			{
				vector<T> v1(v);
				Swap(v1);
			}
			return *this;
		}
		
		void Swap(vector <T>& v)
		{
			swap(_start, v._start);
			swap(_finish, v._finish);
			swap(_endofstorage, v._endofstorage);
		}


		size_t size()const
		{
			return _finish - _start;
		}
		size_t capacity()const
		{
			return _endofstorage - _start;
		}
	private:
		T* _start;
		T* _finish;
		T* _endofstorage;
	};
}