operator==(std::common_iterator)

 

C++

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Freestanding and hosted

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Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

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Filesystem library(C++17)

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Technical specifications

Symbols index

External libraries

 

Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
Stream iterators istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	Iterator customization points ranges::iter_move (C++20) ranges::iter_swap (C++20)
Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

std::common_iterator

Member functions

common_iterator::common_iterator

common_iterator::operator=

common_iterator::operator*common_iterator::operator->

common_iterator::operator++common_iterator::operator++(int)

Non-member functions

operator== (C++20)

operator- (C++20)

iter_move (C++20)

iter_swap (C++20)

Helper classes

incrementable_traits<std::common_iterator> (C++20)

iterator_traits<std::common_iterator> (C++20)

 

template<class I2, std::sentinel_for<I> S2>     requires std::sentinel_for<S, I2> friendconstexprbool operator==(const common_iterator& x,                                   conststd::common_iterator<I2, S2>& y );	(1)	(since C++20)
template<class I2, std::sentinel_for<I> S2>     requires std::sentinel_for<S, I2>&&std::equality_comparable_with<I, I2> friendconstexprbool operator==(const common_iterator& x,                                   conststd::common_iterator<I2, S2>& y );	(2)	(since C++20)

Compares the iterators and/or sentinels held by underlying std::variant member objects var. Two incomparable iterators or two sentinels are considered equal.

The behavior is undefined if either x or y is in an invalid state, i.e. x.var.valueless_by_exception()|| y.var.valueless_by_exception() is equal to true.

Let i be x.var.index() and j be y.var.index().

1) If i == j (i.e. both x and y hold iterators or both hold sentinels), returns true, otherwise returns std::get<i>(x.var)== std::get<j>(y.var).

2) If i ==1&& j ==1 (i.e. both x and y hold sentinels), returns true, otherwise returns std::get<i>(x.var)== std::get<j>(y.var).

The != operator is synthesized from operator==.

These function templates are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::common_iterator<I> is an associated class of the arguments.

Parameters

x, y

-

iterator adaptors to compare

Return value

true if underlying iterators and/or sentinels are equal.

Example

Run this code

#include <cassert>#include <iterator>   int main(){int a[]{0, 1, 2, 3};   using CI =std::common_iterator<std::counted_iterator<int*>, std::default_sentinel_t>;   CI i1{std::counted_iterator{a +0, 2}}; CI i2{std::counted_iterator{a +1, 2}}; CI i3{std::counted_iterator{a +0, 3}}; CI i4{std::counted_iterator{a +0, 0}}; CI s1{std::default_sentinel}; CI s2{std::default_sentinel};   assert((i1 == i2)==true);assert((i1 == i3)==false);assert((i2 == i3)==false);assert((s1 == s2)==true);assert((i1 == s1)==false);assert((i4 == s1)==true);}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3574	C++20	variant was fully constexpr (P2231R1) but common_iterator was not	also made constexpr

See also

operator- (C++20)

computes the distance between two iterator adaptors (function template)