The bottom simulation implementation of vector

vector Member variables of

What is? vector Well ？ vector Is a variable array size sequence container .（ It is similar to the simulation implementation sequence table ）
Simulate the member variables of the implementation sequence table ： The pointer ,size,capacity.

Simulation Implementation of iterator

iterator begin()
		{
    
			return _start;
		}

		iterator end()
		{
    
			reutrn _finish;
		}

		const_iterator begin() const
		{
    
			return _start;
		}

		const_iterator end() const
		{
    
			reutrn _finish;
		}

obtain size,capacity, Empty operation

When data is not modified , We suggest adding const

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

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

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

reserve and resize Simulation Implementation of （ a key ）

reserve in the light of capacity, When the space to be adjusted is greater than capacity Will be adjusted when , Less than capacity Don't deal with it （ But it may not be adjusted to the specified size ,
Because no matter C++ Compiler or Linux Compilers have their own ways to increase capacity ）
resize Aim at size , If the number to be adjusted is less than size, Just cut off . however The number of adjustments is greater than size, Fill in the data after capacity expansion

void reserve(size_t n)
		{
    
			if (n > capacity())
			{
    
				size_t sz = size();
				T* tmp = new T[n];
				//memcpy(tmp,_start,sizeof(T)*size())  If you use memcpy There will be some mistakes 
				// Put this at the end 
				if (_start)
				{
    
					for (size_t i = 0; i < sz; i++)
					{
    
						tmp[i] = _start[i];
					}

					delete[] _start;
				}
				_start = tmp;
				_finish = _start + sz;    // there _finis , _endofstorage All need to refresh 
				_endofstorage = _start + n;
			}
		}

		void resize(size_t n, const T& val = T())
		{
    
			if (n < size())
			{
    
				_finish = _start + n;
			}

			else
			{
    
				if (n > capacity())
				{
    
					reserve(n);
			    }

				while (size() < n)
				{
    
					*_finish++ = val;
				}
			}
		}

pop_back （ Deletion at the end ） and push_back（ Tail insertion ）

void push_back(const T& val)
		{
    
			if (_finish == _endofstorage)  // Here is to judge whether it is full , Do not use _start To compare 
			{
    
				size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newcapacity);
			}
			
			*_finish = val;
			_finish++;
		}

		void pop_back()
		{
    
			if (empty())
			{
    
				cout << "no data to delete" << endl;
				return;
			}
			else
			{
    
				_finish--;
			}
		}

insert（ Insertion at any position ） and erase （ Delete anywhere ）

         iterator insert(iterator pos, const T& val)
		{
    
			if (_finish == _endofstorage)
			{
    
				size_t len = pos - _start;
				size_t newcapacity = capacity() == 0 ? 4 : capacity() * 2;
				reserve(newcapacity);

				// If capacity expansion occurs here ,pos Just refresh 
				// Otherwise it will fail 
				pos = _start + len;
			}

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

			return pos;
		}

		void insert(iterator pos,size_t n ,const T& val)
		{
    
			size_t max = n + size();
			if ( max > capacity())
			{
    
				size_t len = pos - _start;

				reserve(max);

				// If capacity expansion occurs here ,pos Just refresh 
				// Otherwise it will fail 
				pos = _start + len;
			}

			size_t len = n;
			iterator it = _finish - 1;
			while (it >= pos)
			{
    
				*(it + len) = *it;
				it--;
			}

			while (n)
			{
    
				n--;
				*pos = val;
				pos++;
			}

			_finish = _finish + len;
		}

		iterator erase(iterator pos)
		{
    
			if (empty())
			{
    
				cout << " no data to delete" << endl;
			}
            
			iterator it = pos ;
			while (it < _finish-1)
			{
    
				*it = *(it + 1);
				it++;
			}
			_finish--;
			return pos;
		}

structure , destructor , Copy structure , Assignment overload

vector()
			:_start(nullptr)
		    , _finish(nullptr)
			,_endofstorage(nullptr)
			{
    }

		vector(size_t n, const T& val = T())
			:_start(nullptr)
			, _finish(nullptr)
			, _endofstorage(nullptr)
		{
    
			_start = new T[n];
			for (size_t i = 0; i < n; i++)
			{
    
				_start[i] = val;
			}
			_finish = _start + n;
			_endofstorage = _start + n;
		}

		// v1(v2)
		vector(const vector<T>& v)
			:_start(nullptr)
			, _finish(nullptr)
			, _endofstorage(nullptr)
		{
    
			_start = new T[v.capacity()];
			for (size_t i = 0; i < v.size(); i++)
			{
    
				_start[i] = v._start[i];
			}
			_finish = _start + v.size();
			_endofstorage = _start + v.capacity();
		}

		//v1 = v2
		vector<T>& operator=(vector<T> v)
		{
    
			swap(v);
			return *this;
		}
		
        // Template functions in class templates 
		template<class InputIterator>
		vector(InputIterator first, InputIterator last)
		{
    
			int len = last - first;
			_start =_finish = new T[len];
			while (first != last)
			{
    
				*_finish++ = *first++;
			}
			_endofstorage = _start + len;
		}

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

About using when expanding memcpy Some problems will be caused

summary ： If resource management is involved in the object , Never use memcpy Copy between objects , because memcpy yes
Shallow copy , Otherwise, it may cause memory leakage and even program crash .