vector的实现

主要谈一下reserve，insert与ersert中的问题

1.reserve

void reserve(size_t n)
{
	if (n > capacity())
	{
		size_t old_size = size();
		T* tmp = new T[n];
		if (_start)
		{
			//memcpy(tmp, _start, end());
			for (size_t i = 0; i < old_size; i++)
			{
				tmp[i] = _start[i];
			}
			delete[] _start;
		}
		_start = tmp;
		//_finsh = _start + size();
		_finish = _start + old_size;
		_endofstorage = _start + n;
	}
}

这里有几个需要注意的
1.这里不能用memcpy进行拷贝，例如初始化vecetor时memcpy只进行了浅拷贝，而用赋值调用operator =调用深拷贝
2.这里的_finish = _start + size()；是错误的因为此时_start是新的而size()中的_finish仍是旧的

2.insert,ersert

iterator 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++;

	return pos;
}

iterator erase(iterator pos)
{
	assert(pos >= _start);
	assert(pos < _finish);

	iterator it = pos + 1;
	while (it != _finish)
	{
		*(it - 1) = *it;
		++it;
	}

	--_finish;

	return pos;
}

这两个主要是迭代器失效的问题
1.在insert中因为reserve导致pos已经改变需要重新赋值pos = _start + len;
2.在erase中因为删除元素导致整体元素前移pos实际指向的是原来的pos+1，在VS中会强制检查发现迭代器失效。
解决方法是返回正确的新迭代器

以下是常见的功能实现

#include<assert.h>
#include<algorithm>
using namespace std;
namespace LL
{
	template<class T>
	class vector
	{
	public:
		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;
		}

		// 强制编译器生成默认构造
		vector() = default;

		vector(initializer_list<T> il)
		{
			reserve(il.size());
			for (auto& e : il)
			{
				push_back(e);
			}
		}

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

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

		// v1 = v2
		vector<T>& operator=(vector<T> v)
		{
			swap(v);
			return *this;
		}

		// 函数模板
		// 任意类型容器迭代器初始化
		template <class InputIterator>
		vector(InputIterator first, InputIterator last)
		{
			while (first != last)
			{
				push_back(*first);
				++first;
			}
		}

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


		void reserve(size_t n)
		{
			if (n > capacity())
			{
				size_t old_size = size();
				T* tmp = new T[n];
				if (_start)
				{
					//memcpy(tmp, _start, end());
					for (size_t i = 0; i < old_size; i++)
					{
						tmp[i] = _start[i];
					}
					delete[] _start;
				}
				_start = tmp;
				//_finsh = _start + size();
				_finish = _start + old_size;
				_endofstorage = _start + n;
			}
		}

		void resize(size_t i, T val = T())
		{
			if (i > size())
			{
				reserve(i);
				while (_finish!= _start + i)
				{
					*_finish = val;
					_finish++;
				}
			}
			else
			{
				_finish = _start + i;
			}
		}

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

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

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

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

		void clear()
		{
			_finish = _start;
		}

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

		void pop_back()
		{
			//assert(_finish > _start);
			assert(!empty());

			--_finish;
		}

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

		iterator 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++;

			return pos;
		}

		iterator erase(iterator pos)
		{
			assert(pos >= _start);
			assert(pos < _finish);

			iterator it = pos + 1;
			while (it != _finish)
			{
				*(it - 1) = *it;
				++it;
			}

			--_finish;

			return pos;
		}

	private:
		iterator _start = nullptr;
		iterator _finish = nullptr;
		iterator _endofstorage = nullptr;
	};
}