std::input_or_output_iterator - cppreference.com

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 not (possibly cv-qualified) void.

Notes

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.

*i is required to be equality-preserving, although the increment operations required by weakly_incrementable are not.

Example

A minimum iterator.

#include <cstddef>
#include <iterator>

struct SimpleIterator
{
    using difference_type = std::ptrdiff_t;
    
    int operator*();
    
    SimpleIterator& operator++();
    void operator++(int) { ++*this; }
};

static_assert(std::input_or_output_iterator<SimpleIterator>);