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## Concept InputIterator

InputIterator

## Description

An input iterator is an iterator that can read through a sequence of values. It is single-pass (old values of the iterator cannot be re-used), and read-only.

An input iterator represents a position in a sequence. Therefore, the iterator can point into the sequence (returning a value when dereferenced and being incrementable), or be off-the-end (and not dereferenceable or incrementable).

## Refinement of

- Assignable

- DefaultConstructible

- EqualityComparable

## Associated types

- value_type

      std::iterator_traits<Iter>::value_type

  The value type of the iterator (not necessarily what `*i` returns)

- difference_type

      std::iterator_traits<Iter>::difference_type

  The difference type of the iterator

- category

      std::iterator_traits<Iter>::iterator_category

  The category of the iterator

## Notation

Iter
  A type playing the role of iterator-type in the InputIterator concept.
`i`, `j`
  Objects of type Iter
`x`
  Object of type value_type

## Type expressions

Category tag

  category must be derived from std::input_iterator_tag, a model of DefaultConstructible, and a model of CopyConstructible.

Value type copy constructibility

  value_type must be a model of CopyConstructible.

Difference type properties

  difference_type must be a model of SignedInteger.

## Valid expressions

Name | Expression | Type | Precondition | Semantics | Postcondition
--- | --- | --- | --- | --- | ---
Dereference | *i | Convertible to value_type | `i` is incrementable (not off-the-end) |  |
Preincrement | ++i | Iter & | `i` is incrementable (not off-the-end) |  |
Postincrement | i++ |  | `i` is incrementable (not off-the-end) | Equivalent to `(void)(++i)` | `i` is dereferenceable or off-the-end
Postincrement and dereference | *i++ | Convertible to value_type | `i` is incrementable (not off-the-end) | Equivalent to `{value_type t = *i; ++i; return t;}` | `i` is dereferenceable or off-the-end

## Complexity

All iterator operations must take amortized constant time.

## Models

- std::istream_iterator

## See also

- DefaultConstructible

- EqualityComparable

- ForwardIterator

- OutputIterator