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
转载于:https://www.cnblogs.com/vsuu/p/4314427.html
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