C++标准库之迭代器

迭代器是对指针进行进一步抽象的产物。

迭代器是遍历所有容器（序列）/流的统一界面，是标准库泛形算法的基础。

迭代器根据其能力分为五种：

category				properties	valid expressions
all categories				copy-constructible, copy-assignable and destructible	X b(a); b = a;
				Can be incremented	++a a++
Random Access	Bidirectional	Forward	Input	Supports equality/inequality comparisons	a == b a != b
				Can be dereferenced as an rvalue	*a a->m
			Output	Can be dereferenced as an lvalue  (only for mutable iterator types)	*a = t *a++ = t
				default-constructible	X a; X()
				Multi-pass: neither dereferencing nor incrementing affects dereferenceability Multi-pass是指，迭代器不管进行多少次自增及解引用，都不会使得其指过的对象无法访问。	{ b=a; *a++; *b; }
				Can be decremented	--a a-- *a--
				Supports arithmetic operators + and -	a + n n + a a - n a - b
				Supports inequality comparisons (<, >, <= and >=) between iterators	a < b a > b a <= b a >= b
				Supports compound assignment operations += and -=	a += n a -= n
				Supports offset dereference operator ([])	a[n]

辅助函数

template <class InputIterator, class Distance>
void advance (InputIterator& it, Distance n);

　　　it跳转到与原始指向相隔n的另一个元素。it为双向迭代器、随机访问的情况下n可以为负数，否则n只能为正数。表示的概念为it+=n

template<class InputIterator>
typename iterator_traits<InputIterator>::difference_type
distance (InputIterator first, InputIterator last);

　　计算 first 与 last 之间的迭代器个数

template <class BidirectionalIterator>
BidirectionalIterator prev (BidirectionalIterator it,
typename iterator_traits<BidirectionalIterator>::difference_type n = 1);

　　表示的概念为 it - n

template <class ForwardIterator>
ForwardIterator next (ForwardIterator it,
typename iterator_traits<ForwardIterator>::difference_type n = 1);

　　表示的概念为 it + n

迭代器产生器

template <class Container>
back_insert_iterator<Container> back_inserter (Container& x);

　　生成输出迭代器，*it = x 调用Container.push_back(x)实现

template <class Container>
front_insert_iterator<Container> front_inserter (Container& x);

　　生成输出迭代器，*it = x 调用Container.push_front(x) 实现

template <class Container>
insert_iterator<Container> inserter (Container& x, typename Container::iterator it);

　　生成输出迭代器，*it = x 调用Container.insert(it,x)实现

迭代器适配器，将迭代器包装成move_iterator

template <class Iterator>
move_iterator<Iterator> make_move_iterator (Iterator it);

　　生成输入迭代器，将迭代器包装成move_iterator。*it = std::move(*it)

template <class OutputIterator, class T>
class raw_storage_iterator;

　　将未初始化的内存包装成输出迭代器,使其可以像已经初始化的内存一样调用 *it=x

获取迭代器属性

　　iterator_traits<iter>::value_type

　　iterator_traits<iter>::reference

　　iterator_traits<iter>::pointer

　　iterator_traits<iter>::difference_type

　　iterator_traits<iter>::iterator_category