NAME¶

std::input_iterator - std::input_iterator

Synopsis¶

Defined in header <iterator>
template< class I >

concept input_iterator =
std::input_or_output_iterator<I> &&
std::indirectly_readable<I> && (since C++20)
requires { typename /*ITER_CONCEPT*/<I>; } &&

std::derived_from</*ITER_CONCEPT*/<I>,
std::input_iterator_tag>;

The input_iterator concept is a refinement of input_or_output_iterator, adding the
requirement that the referenced values can be read (via indirectly_readable) and the
requirement that the iterator concept tag be present.

Notes¶

Unlike the LegacyInputIterator requirements, the input_iterator concept does not
require equality_comparable, since input iterators are typically compared with
sentinels.

Example¶

A minimum input iterator.

#include <cstddef>
#include <iterator>

struct SimpleInputIterator
{
using difference_type = std::ptrdiff_t;
using value_type = int;

int operator*() const;

SimpleInputIterator& operator++();
void operator++(int) { ++*this; }
};

static_assert(std::input_iterator<SimpleInputIterator>);

See also¶

input_or_output_iterator specifies that objects of a type can be incremented and
(C++20) dereferenced
(concept)
forward_iterator specifies that an input_iterator is a forward iterator,
(C++20) supporting equality comparison and multi-pass
(concept)