Defined in header <iterator>
template <class I>
concept input_or_output_iterator =
  requires(I i) {
    { *i } -> /*can-reference*/;
  } &&
(since C++20)

The input_or_output_iterator concept forms the basis of the iterator concept taxonomy; every iterator type satisfies the input_or_output_iterator requirements.

The exposition-only concept /*can-reference*/ is satisfied if and only if the type is referenceable (in particular, not void).

Equality preservation

Expressions declared in requires-expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).


input_or_output_iterator itself only specifies operations for dereferencing and incrementing an iterator. Most algorithms will require additional operations, for example:

Unlike the LegacyIterator requirements, the input_or_output_iterator concept does not require copyability.

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