6.用c++实现stl中的vector

#include 
#include 
using namespace std;


template
class vector
{
public:
	vector(int size=10)
	{
		_first = new T[size];
		_last = _first;
		_end = _first + size;
	}
	~vector()
	{
		delete[]_first;
		_first = _last = _end = nullptr;
	}
	vector(const vector& rhs)
	{
		int size = rhs._end - rhs._first;
		_first = new T[size];
		int len = rhs._last - rhs._first;
		for (int i = 0; i < len; i++)
		{
			_first[i] = rhs._first[i];

		}
		_last = _first + len;
		_end = _first + size;
	}

	vector& operator=(const vector& rhs)
	{
		if (this == &rhs)
			return *this;
		delete[] _first;

		int size = rhs._end - rhs._first;
		_first = new T[size];
		int len = rhs._last - rhs._first;
		for (int i = 0; i < len; i++)
		{
			_first[i] = rhs._first[i];

		}
		_last = _first + len;
		_end = _first + size;
	}

	void push_back(T val) //向容器末尾添加元素
	{
		if (full())
			expand();
		*_last++ = val;
	}
	void pop_back()	//从容器末尾删除元素
	{
		if (empty())
			return;
		--_last;
	}
	T back()const //返回容器末尾元素的值
	{
		return *(_last - 1);
	}
	bool full() const
	{
		return _last == _end;
	}
	bool empty() const
	{
		return _first == _last;
	}
	int size()const
	{
		return _last - _first;
	}

private:
	T* _first;	//指向数组的起始位置
	T* _last;	//指向数组中有效元素的后继位置
	T* _end;	//指向数组空间的后继位置

	void expand() //容器的二倍扩容操作
	{
		int size = _end - _first;
		T* ptmp = new T[2 * size];
		for (int i = 0; i < size; i++)
		{
			ptmp[i] = _first[i];
		}
		delete[]_first;
		_first = ptmp;
		_last = _first + size;
		_last = _first + 2 * size;
	}
};


int main()
{
	vectorvec;
	for (int i = 0; i < 10; i++)
	{
		vec.push_back(rand() % 100);
	}

	vec.pop_back();

	while (!vec.empty())
	{
		cout << vec.back() << " ";
		vec.pop_back();
	}
	cout << endl;
	return 0;
}