std::input_or_output_iterator

template< class I >
    concept input_or_output_iterator =
        requires(I i) {
            { *i } -> /*can-reference*/;
        } &&
        std::weakly_incrementable<I>;

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).

Notes

A typical input_or_output_iterator class only needs to be movable, and provide the following members:

• Member typedef difference_type (used by std::iter_difference_t).
• Prefix operator++ that returns a reference to *this.
• Postfix operator++.
• The dereference operator operator*.

Alternatively, the difference_type can be provided by specializing either std::iterator_traits or std::incrementable_traits. The functions can be defined as non-members, to be found by argument-dependent lookup.

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

• comparing iterators with sentinels (see sentinel_for);
• reading values from an iterator (see indirectly_readable and input_iterator);
• writing values to an iterator (see indirectly_writable and output_iterator);
• a richer set of iterator movements (see forward_iterator, bidirectional_iterator, random_access_iterator).

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