C++ STL中vector的模拟实现

目录

1.四个默认函数

2.迭代器

3.访问

4.插入删除

4.空间扩容

5.访问数据个数，空间大小

6.交换

1.四个默认函数

        //4个默然函数
		//vecotr<int> v
		vector()
		:_start(nullptr)
		,_finish(nullptr)
		,_endofstorage(nullptr)
		{}

		template <class InputIterator >
		vector(InputIterator  first, InputIterator  finish)
		: _start(nullptr)
		, _finish(nullptr)
		, _endofstorage(nullptr)
		{
			while (first != finish)
			{
				push_back(*first);

				first++;
			}
		}


		
		vector(const vector& v)
		{
			
			_start = new T[v.capacity()];
			_finish = _start + v.size();
			_endofstorage = _start + v.capacity();

			int i = 0;
			while (i < v.size())
			{
				(*this)[i] = v[i];
				i++;
			}
		}

		vector operator=(vector v) //这里不用引用就是要复用上面的拷贝构造
		{
			swap(v);
			return *this;
		}
			
		~vector()
		{
			delete[] _start;
			_start = _finish = _endofstorage = nullptr;
		}

2.迭代器

        //迭代器
		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;
		}

3.访问

        //访问
		T& operator[](size_t pos)
		{
			return *(_start + pos);
		}
		const T& operator[](size_t pos) const
		{
			return *(_start + pos);
		}

4.插入删除

void push_back(const T& val)//const 引用用好，是自定义类型的时候提高效率
		{
			if (_finish == _endofstorage)  //需要扩容    
			{
				capacity() == 0 ? reserve(4) : reserve(size() * 2);

			}
			
			*_finish = val;
			_finish++;
			
		}


		iterator insert(iterator pos, const T& val)   
		{ 
			
			
			if (_finish == _endofstorage)  //需要扩容
			{
				if (_finish == nullptr) //第一次插入
				{
					_start = new T[4];
					_finish = _start;
					_endofstorage = _start + 4;
					*_finish = val;
					_finish++;
					pos = begin();
				}
				else  //不是第一次插入
				{
					size_t old = pos - _start;
					reserve(capacity() * 2);
					pos = _start + old; //不然pos会失效

					//挪动
					iterator tail = _finish;
					while (tail != pos)
					{
						*tail = *(tail - 1);
						tail--;
					}

					*pos = val;
					_finish++;
					
				}
			}
			else
			{
				//挪动
				iterator tail = _finish;
				while (tail != pos)
				{
					*tail = *(tail - 1);
					tail--;
				}

				*pos = val;
				_finish++;
				
			}
			return pos;
		}


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

			return pos;
		}

4.空间扩容

void resize(size_t n, T val = T())    
		{
			if (n > size())
			{
				if (n > capacity())
				{
					reserve(n);
				}
				size_t a = size();
				size_t b = capacity();
				int i = 0;
				size_t sz = size();
				
				while (i < n - sz)
				{
					push_back(val);
					i++;
					
				}
				size_t aa = size();
				size_t bb = capacity();

			}
			else 
			{
				int i = 0;
				while (i < size() - n)
				{
					_finish--;
				}
			}
			
		}


        void reserve(size_t n)
		{
			if (n > _endofstorage - _start)
			{
				size_t sz = size();
				T* tem = new T[n];
				int i = 0;
				if (_start)
				{
					while (i < sz)
					{
						tem[i] = (*this)[i];
						i++;
					}
					delete[] _start; 
				}

				_start = tem;
				_finish = _start + sz;
				_endofstorage = _start + n;
			}
		}

5.访问数据个数，空间大小

		//访问个数
		size_t size() const 
		{
			return _finish - _start;
		}
		size_t capacity() const
		{
			return _endofstorage - _start;
		}

		

6.交换

        //交换
		void swap(vector& v)
		{
			std::swap(_start, v._start);
			std::swap(_finish, v._finish);
			std::swap(_endofstorage, v._endofstorage);
		}