NAME¶

std::forward_iterator - std::forward_iterator

Synopsis¶

Defined in header <iterator>
template< class I >

concept forward_iterator =
std::input_iterator<I> &&
std::derived_from</*ITER_CONCEPT*/<I>, (since C++20)
std::forward_iterator_tag> &&
std::incrementable<I> &&

std::sentinel_for<I, I>;

This concept refines std::input_iterator by requiring that I also model
std::incrementable (thereby making it suitable for multi-pass algorithms), and
guaranteeing that two iterators to the same range can be compared against each
other.

Notes¶

Unlike the LegacyForwardIterator requirements, the forward_iterator concept does not
require dereference to return a reference.

Example¶

A minimum forward iterator.

#include <cstddef>
#include <iterator>

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

int operator*() const;

SimpleForwardIterator& operator++();

SimpleForwardIterator operator++(int)
{
auto tmp = *this;
++*this;
return tmp;
}

bool operator==(const SimpleForwardIterator&) const;
};

static_assert(std::forward_iterator<SimpleForwardIterator>);

See also¶

specifies that a type is an input iterator, that is, its
input_iterator referenced values can be read and it can be both pre- and
(C++20) post-incremented
(concept)
bidirectional_iterator specifies that a forward_iterator is a bidirectional
(C++20) iterator, supporting movement backwards
(concept)