operator==(std::common_iterator)

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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)
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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)
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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)
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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::common_iterator

成员函数

common_iterator::common_iterator

common_iterator::operator=

common_iterator::operator*common_iterator::operator->

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

非成员函数

operator== (C++20)

operator- (C++20)

iter_move (C++20)

iter_swap (C++20)

辅助类

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

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

 

<tbody> </tbody>

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

比较底层 std::variant 成员对象 var 所保有的迭代器与/或哨位。认为两个不可比较的迭代器或两个哨位相等。

若 x 或 y 处于无效状态，即 x.var.valueless_by_exception() || y.var.valueless_by_exception() 等于 true，则行为未定义。

令 i 为 x.var.index()，j 为 y.var.index()。

1) 若 i == j（即 x 与 y 均保有迭代器或哨位）则返回 true，否则返回 std::get<i>(x.var) == std::get<j>(y.var)；

2) 若 i == 1 && j == 1（即 x 与 y 均保有哨位）则返回 true，否则返回 std::get<i>(x.var) == std::get<j>(y.var)。

!= 运算符从 operator== 运算符合成。

这些函数模板对常规的无限定或有限定查找不可见，而只能在 std::common_iterator<I> 为实参的关联类时由实参依赖查找找到。

参数

x, y

-

要比较的迭代器适配器

返回值

若底层迭代器与/或哨位相等则为 true。

示例

运行此代码

#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);
}

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
LWG 3574	C++20	variant 为完全 constexpr (P2231R1) 但 common_iterator 不是	亦使之为 constexpr

参阅

operator- (C++20)

计算两个迭代器适配器间的距离 (函数模板)