# std::experimental::ranges::input_iterator_tag, std::experimental::ranges::output_iterator_tag, std::experimental::ranges::forward_iterator_tag, std::experimental::ranges::bidirectional_iterator_tag, std::experimental::ranges::random_access_iterator_tag

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< cpp‎ | experimental‎ | ranges

Defined in header `<experimental/ranges/iterator>` |  |
struct input_iterator_tag { }; |  |
struct output_iterator_tag { }; |  |
struct forward_iterator_tag : public input_iterator_tag { }; |  |
struct bidirectional_iterator_tag : public forward_iterator_tag { }; |  |
struct random_access_iterator_tag : public bidirectional_iterator_tag { }; |  |

Defines the category of an iterator. Each tag is an empty type and corresponds to one of the five iterator categories:

- `input_iterator_tag` corresponds to `InputIterator`.
- `forward_iterator_tag` corresponds to `ForwardIterator`.
- `bidirectional_iterator_tag` corresponds to `BidirectionalIterator`.
- `random_access_iterator_tag` corresponds to `RandomAccessIterator`.
- `output_iterator_tag` corresponds to `OutputIterator`; it is not used and provided solely for backward compatiblity.

Iterator category tags carry information that can be used to select the most efficient algorithms for the specific requirement set that is implied by the category. However, concept-based overloading is preferred.

For every `InputIterator` type `I`, ranges::iterator_category_t<I> must be defined to be an alias for the most specific category tag that describes the iterator's behavior.

### Example

| This section is incomplete Reason: no example

### See also

input_iterator_tag output_iterator_tag forward_iterator_tag bidirectional_iterator_tag random_access_iterator_tag contiguous_iterator_tag (C++20) | empty class types used to indicate iterator categories (class)
iterator_traits | compatibility traits class that collects an iterator’s associated types (alias template)

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