operator-(std::common_iterator)

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

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< std::sized_sentinel_for<I> I2, std::sized_sentinel_for<I> S2 >     requires std::sized_sentinel_for<S, I2> friend constexpr std::iter_difference_t<I2>     operator-( const common_iterator& x, const std::common_iterator<I2, S2>& y );		(since C++20)

Computes the distance between two iterator adaptors. Two sentinels are considered equal.

Let var denote the underlying std::variant member object in std::common_iterator, the behavior is undefined if either x or y is invalid, i.e. x.var.valueless_by_exception() || y.var.valueless_by_exception() is true.

This function template is 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 compute the difference of

Return value

• ​0​ if x.var holds an S object and y.var holds an S2 object, i.e. both of them hold a sentinel.
• Otherwise, alt_x - alt_y, where alt_x and alt_y are the alternatives held by x.var and y.var, respectively (either two iterators or one iterator and one sentinel).

Example

Run this code

#include <algorithm>
#include <iostream>
#include <iterator>
 
int main()
{
    int a[]{0, 1, 2, 3, 4, 5};
 
    using CI = std::common_iterator<
                   std::counted_iterator<int*>,
                   std::default_sentinel_t
                   >;
 
    CI i1{std::counted_iterator{a + 1, 2}};
    CI i2{std::counted_iterator{a, 3}};
    CI s1{std::default_sentinel};
    CI s2{std::default_sentinel};
 
    std::cout << (s2 - s1) << ' '
              << (i2 - i1) << ' '
              << (i1 - s1) << '\n';
}

Output:

0 -1 -2

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++operator++(int) (C++20)

advances the iterator adaptor (public member function)