STL — vector源代码剖析

template <class T, class Alloc = alloc>
class vector {
public:

	//迭代器的五种类型
	typedef T value_type;
	typedef value_type* pointer;
	typedef const value_type* const_pointer;

	typedef value_type* iterator;
	typedef const value_type* const_iterator;

	typedef value_type& reference;
	typedef const value_type& const_reference;

	typedef size_t size_type;

	typedef ptrdiff_t difference_type;

#ifdef __STL_CLASS_PARTIAL_SPECIALIZATION
	typedef reverse_iterator<const_iterator> const_reverse_iterator;
	typedef reverse_iterator<iterator> reverse_iterator;
#else /* __STL_CLASS_PARTIAL_SPECIALIZATION */
	typedef reverse_iterator<const_iterator, value_type, const_reference,
		difference_type>  const_reverse_iterator;
	typedef reverse_iterator<iterator, value_type, reference, difference_type>
		reverse_iterator;
#endif /* __STL_CLASS_PARTIAL_SPECIALIZATION */
protected:

	//在这里就用到了我们的空间配置器.
	typedef simple_alloc<value_type, Alloc> data_allocator; //前面是有博客的

	//这里vector维护3个迭代器. 分别指向申请到内存的头部，vector利用到的地方 和 vector申请到内存结束的地方.
	iterator start; //头.
	iterator finish;//使用位置.
	iterator end_of_storage;//申请到内存结束的地方.


	void insert_aux(iterator position, const T& x);
	void deallocate() {
		if (start) data_allocator::deallocate(start, end_of_storage - start);
	}

	void fill_initialize(size_type n, const T& value) {
		start = allocate_and_fill(n, value);
		finish = start + n;
		end_of_storage = finish;
	}
public:
	//这些begin end rend rbegin 不解释！
	iterator begin() { return start; }
	const_iterator begin() const { return start; }
	iterator end() { return finish; }
	const_iterator end() const { return finish; }
	reverse_iterator rbegin() { return reverse_iterator(end()); }
	const_reverse_iterator rbegin() const {
		return const_reverse_iterator(end());
	}
	reverse_iterator rend() { return reverse_iterator(begin()); }
	const_reverse_iterator rend() const {
		return const_reverse_iterator(begin());
	}

	size_type size() const { return size_type(end() - begin()); } //元素个数
	size_type max_size() const { return size_type(-1) / sizeof(T); } //最大元素个数
	size_type capacity() const { return size_type(end_of_storage - begin()); } //容量
	bool empty() const { return begin() == end(); } //是否为空
	reference operator
		[](size_type n) {
		return *(begin() + n);
	}
	const_reference operator[](size_type n) const { return *(begin() + n); } //支持随机访问.

	vector() : start(0), finish(0), end_of_storage(0) {}
	vector(size_type n, const T& value) { fill_initialize(n, value); }
	vector(int n, const T& value) { fill_initialize(n, value); }
	vector(long n, const T& value) { fill_initialize(n, value); }
	explicit vector(size_type n) { fill_initialize(n, T()); }

	vector(const vector<T, Alloc>& x) {
		start = allocate_and_copy(x.end() - x.begin(), x.begin(), x.end());
		finish = start + (x.end() - x.begin());
		end_of_storage = finish;
	}

#ifdef __STL_MEMBER_TEMPLATES
	template <class InputIterator>
	vector(InputIterator first, InputIterator last) :
		start(0), finish(0), end_of_storage(0)
	{
		range_initialize(first, last, iterator_category(first));
	}
#else /* __STL_MEMBER_TEMPLATES */
	vector(const_iterator first, const_iterator last) {
		size_type n = 0;
		distance(first, last, n);
		start = allocate_and_copy(n, first, last);
		finish = start + n;
		end_of_storage = finish;
	}
#endif /* __STL_MEMBER_TEMPLATES */
	~vector() { //这是vector的一个member function
		destroy(start, finish);
		deallocate();
	}

	reference front() { return *begin(); } //第一个元素的引用.
	const_reference front() const { return *begin(); } 
	reference back() { return *(end() - 1); } //最后一个元素的引用.
	const_reference back() const { return *(end() - 1); }
	void push_back(const T& x) {
		if (finish != end_of_storage) {
			construct(finish, x);
			++finish;
		}
		else
			insert_aux(end(), x);
	}
	void insert(iterator pos, size_type n, const T& x);
	void pop_back() {
		--finish;
		destroy(finish);
	}
	iterator erase(iterator position) {
		if (position + 1 != end())
			copy(position + 1, finish, position);
		--finish;
		destroy(finish);
		return position;
	}
	void resize(size_type new_size) { resize(new_size, T()); }
	void clear() { erase(begin(), end()); }

protected:
	//配置空间并且填满内容.
	iterator allocate_and_fill(size_type n, const T& x) {
		iterator result = data_allocator::allocate(n);
		__STL_TRY{
			uninitialized_fill_n(result, n, x);
			return result;
		}
		__STL_UNWIND(data_allocator::deallocate(result, n));
	}

vector(size_type n, const T& value) { fill_initialize(n, value); }

void fill_initialize(size_type n, const T& value) {//填充并初始化
	start = allocate_and_fill(n, value);
	finish = start + n;
	end_of_storage = finish;
}

iterator allocate_and_fill(size_type n, const T& x) {//配置而后填充
	iterator result = data_allocator::allocate(n);
	__STL_TRY{
		uninitialized_fill_n(result, n, x);
		return result;
	}
	__STL_UNWIND(data_allocator::deallocate(result, n));
}

void push_back(const T& x) {
	if (finish != end_of_storage) {
		construct(finish, x);
		++finish;
	}
	else
		insert_aux(end(), x);
}

template <class T, class Alloc>
void vector<T, Alloc>::insert_aux(iterator position, const T& x) {
	if (finish != end_of_storage) { //还有备用空间
		//在备用空间起始处构造一个函数，并以vector最后一个元素值为其初值.
		construct(finish, *(finish - 1));
		++finish;
		T x_copy = x;
		copy_backward(position, finish - 2, finish - 1);
		*position = x_copy;
	}
	else { //已无备用空间

		const size_type old_ size = size();
		const size_type len = old_size != 0 ? 2 * old_size : 1; //这句仔细看！！！！
		iterator new_start = data_allocator::allocate(len); //实际配置的空间.
		iterator new_finish = new_start;
		__STL_TRY{
			//将原vector的内容拷贝至新的vector.
			new_finish = uninitialized_copy(start, position, new_start);
			//为新元素设定初值x.
			construct(new_finish, x);
			++new_finish;

			//将安插点的原内容也拷贝过来.
			new_finish = uninitialized_copy(position, finish, new_finish);
		}

#       ifdef  __STL_USE_EXCEPTIONS 
		catch (...) {
			//析构并释放原vector
			destroy(new_start, new_finish);
			data_allocator::deallocate(new_start, len);
			throw;
		}
#       endif /* __STL_USE_EXCEPTIONS */

		//调整迭代器，指向新的vector.
		destroy(begin(), end());
		deallocate();
		start = new_start;
		finish = new_finish;
		end_of_storage = new_start + len;
	}
}

template <class T, class Alloc>
//从position开始，插入n个元素，元素初值为x。
void vector<T, Alloc>::insert(iterator position, size_type n, const T& x) {
	if (n != 0) { //当n != 0的时候 才进行以下所有操作
		if (size_type(end_of_storage - finish) >= n) {
			//备用空间大于 等于 "新增元素个数"
			T x_copy = x;
			//以下计算插入点之后的现有元素个数
			const size_type elems_after = finish - position;
			iterator old_finish = finish;
			if (elems_after > n) {
				// 插入点之后的现有元素个数 大于 新增元素个数
				uninitialized_copy(finish - n, finish, finish);
				finish += n;
				copy_backward(position, old_finish - n, old_finish);
				fill(position, position + n, x_copy);
			}
			else {
				// 插入点之后的现有元素个数 小于等于 新增元素个数
				uninitialized_fill_n(finish, n - elems_after, x_copy);
				finish += n - elems_after;
				uninitialized_copy(position, old_finish, finish);
				finish += elems_after;
				fill(position, old_finish, x_copy);
			}
		}
		else {
			//备用空间小于 "新增元素个数"
			//首先决定新长度: 旧长度的两倍，或旧长度+新增元素个数.
			const size_type old_size = size();
			const size_type len = old_size + max(old_size, n);

			//以下配置新的vector空间.
			iterator new_start = data_allocator::allocate(len);
			iterator new_finish = new_start;
			__STL_TRY{
				//以下首先将旧vector的插入点之前的元素复制到新空间
				new_finish = uninitialized_copy(start, position, new_start);
				//以下再将新增元素填入新空间.
				new_finish = uninitialized_fill_n(new_finish, n, x);
				//以下再将就vector的插入点之后的元素复制到新空间.
				new_finish = uninitialized_copy(position, finish, new_finish);
			}
#         ifdef  __STL_USE_EXCEPTIONS 
			catch (...) {
				//以下清楚并释放旧的vector
				destroy(new_start, new_finish);
				data_allocator::deallocate(new_start, len);
				throw;
			}
#         endif /* __STL_USE_EXCEPTIONS */
			destroy(start, finish);
			deallocate();
			start = new_start;
			finish = new_finish;
			end_of_storage = new_start + len;
		}
	}
}