std::basic_const_iterator<Iter>::operator constant-iterator

 

C++

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功能特性测试宏 (C++20)

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符号索引

外部库

 

迭代器库

迭代器概念
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)
迭代器原语
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 (C++17 中弃用) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
算法概念与工具
间接可调用概念
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)
常用算法要求
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)
工具
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
迭代器适配器
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)
流迭代器 istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	迭代器定制点 ranges::iter_move (C++20) ranges::iter_swap (C++20)
迭代器操作 advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	范围访问 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::basic_const_iterator

成员函数

basic_const_iterator::basic_const_iterator

basic_const_iterator::base

basic_const_iterator::operator*basic_const_iterator::operator->

basic_const_iterator::operator[]

basic_const_iterator::operator++basic_const_iterator::operator+=basic_const_iterator::operator--basic_const_iterator::operator-=

basic_const_iterator::operator==basic_const_iterator::operator<basic_const_iterator::operator<=basic_const_iterator::operator>basic_const_iterator::operator>=basic_const_iterator::operator<=>

basic_const_iterator::operator constant-iterator

非成员函数

operator<operator<=operator>operator>= (C++23)(C++23)(C++23)(C++23)

operator+ (C++23)

operator- (C++23)

iter_move(std::basic_const_iterator) (C++23)

辅助类

common_type<std::basic_const_iterator> (C++23)

 

template< /*not-a-const-iterator*/ CI >   requires /*constant-iterator*/<CI> &&       std::convertible_to<Iter const&, CI> constexpr operator CI() const &;	(1)	(C++23 起)
template< /*not-a-const-iterator*/ CI >   requires /*constant-iterator*/<CI> &&       std::convertible_to<Iter, CI> constexpr operator CI() &&;	(2)	(C++23 起)

返回底层迭代器 current 可以显式或隐式转换成的常量迭代器。

当且仅当 CI 不是 basic_const_iterator 的特化时，CI 满足仅用于阐释的概念 /*not-a-const-iterator*/。

返回值

1) current

2) std::move(current)

示例

运行此代码

#include <iterator>
#include <ranges>
#include <vector>
 
void foo(std::vector<int>::const_iterator) {}
 
int main()
{
    auto v = std::vector<int>();
    {
        // 下面的 ranges::cbegin 返回 vector<int>::const_iterator
        auto i1 = std::ranges::cbegin(v);
        foo(i1); // OK
    }
 
    auto t = v | std::views::take_while([](int const x) { return x < 100; });
    {
        // 下面的 ranges::cbegin 返回 basic_const_iterator<vector<int>::iterator>
        auto i2 = std::ranges::cbegin(t);
        foo(i2); // P2836R1 前报错
    }
}

缺陷报告

下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。

缺陷报告	应用于	出版时的行为	正确行为
P2836R1	C++23	basic_const_iterator 不遵守其底层类型的可转换性	提供转换运算符