operator==,!=,<,<=,>,>=,<=>(std::reverse_iterator)

 

C++

编译器支持

自立实现与有宿主实现

语言

标准库

标准库标头

具名要求

功能特性测试宏 (C++20)

语言支持库

概念库 (C++20)

元编程库 (C++11)

诊断库

通用工具库

字符串库

容器库

迭代器库

范围库 (C++20)

算法库

数值库

本地化库

输入/输出库

文件系统库 (C++17)

正则表达式库 (C++11)

并发支持库 (C++11)

技术规范

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) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) 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
iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (C++17 中弃用)	incrementable_traits (C++20) indirectly_readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++20)(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	projected
迭代器适配器
reverse_iterator move_iterator (C++11) 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) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) make_const_iterator (C++23) make_const_sentinel (C++23) back_inserter front_inserter inserter
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) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

std::reverse_iterator

成员函数

reverse_iterator::reverse_iterator

reverse_iterator::operator=

reverse_iterator::base

reverse_iterator::operator*reverse_iterator::operator->

reverse_iterator::operator[]

reverse_iterator::operator++reverse_iterator::operator+reverse_iterator::operator+=reverse_iterator::operator--reverse_iterator::operator-reverse_iterator::operator-=

非成员函数

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

operator+

operator-

iter_move (C++20)

iter_swap (C++20)

 

	(1)
template< class Iterator1, class Iterator2 > bool operator==( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );			(C++17 前)
template< class Iterator1, class Iterator2 > constexpr bool operator==( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );			(C++17 起)
		(2)
template< class Iterator1, class Iterator2 > bool operator!=( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );				(C++17 前)
template< class Iterator1, class Iterator2 > constexpr bool operator!=( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );				(C++17 起)
			(3)
template< class Iterator1, class Iterator2 > bool operator<( const std::reverse_iterator<Iterator1>& lhs,                 const std::reverse_iterator<Iterator2>& rhs );					(C++17 前)
template< class Iterator1, class Iterator2 > constexpr bool operator<( const std::reverse_iterator<Iterator1>& lhs,                           const std::reverse_iterator<Iterator2>& rhs );					(C++17 起)
				(4)
template< class Iterator1, class Iterator2 > bool operator<=( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );						(C++17 前)
template< class Iterator1, class Iterator2 > constexpr bool operator<=( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );						(C++17 起)
					(5)
template< class Iterator1, class Iterator2 > bool operator>( const std::reverse_iterator<Iterator1>& lhs,                 const std::reverse_iterator<Iterator2>& rhs );							(C++17 前)
template< class Iterator1, class Iterator2 > constexpr bool operator>( const std::reverse_iterator<Iterator1>& lhs,                           const std::reverse_iterator<Iterator2>& rhs );							(C++17 起)
						(6)
template< class Iterator1, class Iterator2 > bool operator>=( const std::reverse_iterator<Iterator1>& lhs,                  const std::reverse_iterator<Iterator2>& rhs );								(C++17 前)
template< class Iterator1, class Iterator2 > constexpr bool operator>=( const std::reverse_iterator<Iterator1>& lhs,                            const std::reverse_iterator<Iterator2>& rhs );								(C++17 起)
template<class Iterator1, std::three_way_comparable_with<Iterator1> Iterator2> constexpr std::compare_three_way_result_t<Iterator1, Iterator2>     operator<=>( const std::reverse_iterator<Iterator1>& x,                  const std::reverse_iterator<Iterator2>& y );							(7)	(C++20 起)

比较底层迭代器。考虑到迭代器顺序是逆向的，而应用逆向比较。

(1-6) 只有在底层比较表达式（见后述）为良构且可转换到 bool 时才会参与重载决议。 != 运算符从 == 运算符合成。

(C++20 起)

参数

lhs, rhs

-

要比较的迭代器适配器

返回值

1) lhs.base() == rhs.base()

2) lhs.base() != rhs.base()

3) lhs.base() > rhs.base()

4) lhs.base() >= rhs.base()

5) lhs.base() < rhs.base()

6) lhs.base() <= rhs.base()

7) rhs.base() <=> lhs.base()

示例

运行此代码

#include <compare>
#include <iostream>
#include <iterator>
 
int main()
{
    int a[]{0, 1, 2, 3};
    //            ↑  └───── x, y
    //            └──────── z
 
    std::reverse_iterator<int*>
        x {std::rend(a) - std::size(a)},
        y {std::rend(a) - std::size(a)},
        z {std::rbegin(a) + 1};
 
    std::cout
        << std::boolalpha
        << "*x == " << *x << '\n' // 3
        << "*y == " << *y << '\n' // 3
        << "*z == " << *z << '\n' // 2
        << "x == y ? " << (x == y) << '\n' // true
        << "x != y ? " << (x != y) << '\n' // false
        << "x <  y ? " << (x <  y) << '\n' // false
        << "x <= y ? " << (x <= y) << '\n' // true
        << "x == z ? " << (x == z) << '\n' // false
        << "x != z ? " << (x != z) << '\n' // true
        << "x <  z ? " << (x <  z) << '\n' // true
        << "x <= z ? " << (x <= z) << '\n' // true
        << "x <=> y == 0 ? " << (x <=> y == 0) << '\n' // true
        << "x <=> y <  0 ? " << (x <=> y <  0) << '\n' // false
        << "x <=> y >  0 ? " << (x <=> y >  0) << '\n' // false
        << "x <=> z == 0 ? " << (x <=> z == 0) << '\n' // false
        << "x <=> z <  0 ? " << (x <=> z <  0) << '\n' // true
        << "x <=> z >  0 ? " << (x <=> z >  0) << '\n' // false
        ;
}

输出：

*x == 3
*y == 3
*z == 2
x == y ? true
x != y ? false
x <  y ? false
x <= y ? false
x == z ? false
x != z ? true
x <  z ? true
x <= z ? true
x <=> y == 0 ? true
x <=> y <  0 ? false
x <=> y >  0 ? false
x <=> z == 0 ? false
x <=> z <  0 ? true
x <=> z >  0 ? false

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 280	C++98	只有底层迭代器类型相同的 std::reverse_iterator 才能比较	底层迭代器类型不同的 std::reverse_iterator 也可以比较