NAME¶

std::bidirectional_iterator - std::bidirectional_iterator

Synopsis¶

Defined in header <iterator>
template< class I >

concept bidirectional_iterator =
std::forward_iterator<I> &&
std::derived_from</*ITER_CONCEPT*/<I>,
std::bidirectional_iterator_tag> && (since C++20)
requires(I i) {
{ --i } -> std::same_as<I&>;
{ i-- } -> std::same_as<I>;

};

The concept bidirectional_iterator refines forward_iterator by adding the ability to
move an iterator backward.

Notes¶

Unlike the LegacyBidirectionalIterator requirements, the bidirectional_iterator
concept does not require dereference to return an lvalue.

Example¶

A minimum bidirectional iterator.

#include <cstddef>
#include <iterator>

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

int operator*() const;

SimpleBidiIterator& operator++();

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

SimpleBidiIterator& operator--();

SimpleBidiIterator operator--(int)
{
auto tmp = *this;
--*this;
return tmp;
}

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

static_assert(std::bidirectional_iterator<SimpleBidiIterator>);

See also¶

forward_iterator specifies that an input_iterator is a forward iterator,
(C++20) supporting equality comparison and multi-pass
(concept)
specifies that a bidirectional_iterator is a random-access
random_access_iterator iterator, supporting advancement in constant time and
(C++20) subscripting
(concept)