std::common_iterator<I,S>::operator++

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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)

(C++20)

(C++20)

(C++26)

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)

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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)

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constexpr common_iterator& operator++();	(1)	(since C++20)
constexpr decltype(auto) operator++(int);	(2)	(since C++20)
Helper types
class/postfix_proxy/{ std::iter_value_t<I> keep_; constexpr postfix_proxy(std::iter_reference_t<I>&& x) : keep_(std::forward<std::iter_reference_t<I>>(x)){} public: constexprconststd::iter_value_t<I>& operator*()constnoexcept{ return keep_; } };	(3)	(exposition only*)

Increments the underlying iterator.

The behavior is undefined if the underlyingstd::variant member objectvar does not hold an object of typeI, i.e.std::holds_alternative(var) is equal tofalse.

Letit denote the iterator of typeI held byvar, that isstd::get(var).

1) Pre-increments by one. Equivalent to++it;return*this;.

2) Post-increments by one:

Equivalent to:auto tmp=*this;++*this;return tmp;, ifI modelsforward_iterator.
Equivalent to:return it++;, if the variable definitionauto&& ref=*it++; is well-formed, or either

std::indirectly_readable or
std::constructible_from<std::iter_value_t,std::iter_reference_t> or
std::move_constructible<std::iter_value_t>

isfalse.

Equivalent to:postfix_proxy p(**this);++*this;return p; otherwise, wherepostfix_proxy is an exposition only helper type(3).

[edit]Parameters

(none)

[edit]Return value

1)*this

2) A copy of*this that was made before the change, or a result of post-increment of the underlying iterator, or a proxy keeping the value of the current element, as described above.

[edit]Example

Run this code

#include <algorithm>#include <initializer_list>#include <iostream>#include <iterator> int main(){constauto il={1,2,3,4,5,6}; using CI=std::common_iterator<std::counted_iterator<std::initializer_list<int>::iterator>,std::default_sentinel_t>;     CI first{std::counted_iterator{std::begin(il),std::ssize(il)-2}}; for(; first!=std::default_sentinel;++first)std::cout<<*first<<' ';std::cout<<'\n';}

Output:

1 2 3 4

[edit]Defect reports

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

DR	Applied to	Behavior as published	Correct behavior
P2259R1	C++20	post increment might discard its result in more situations	a proxy class is used to keep the result
LWG 3546	C++20	initialization of the proxy object was sometimes ill-formed	situation and definition adjusted
LWG 3574	C++20	`variant` was fully constexpr (P2231R1) but`common_iterator` was not	also made constexpr
LWG 3595	C++20	functions of the proxy type lacked constexpr and noexcept	added