operator==,<=>(std::counted_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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std::counted_iterator

成员函数

counted_iterator::counted_iterator

counted_iterator::operator=

counted_iterator::base

counted_iterator::count

counted_iterator::operator*counted_iterator::operator->

counted_iterator::operator[]

counted_iterator::operator++counted_iterator::operator++(int)counted_iterator::operator+counted_iterator::operator+=counted_iterator::operator--counted_iterator::operator--(int)counted_iterator::operator-counted_iterator::operator-=

非成员函数

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

operator==(default_sentinel_t) (C++20)

operator+ (C++20)

operator- (C++20)

operator-(default_sentinel_t) (C++20)

iter_move (C++20)

iter_swap (C++20)

辅助类

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

 

template< std::common_with<I> I2 >     friend constexpr bool operator==(         const counted_iterator& x, const counted_iterator<I2>& y );	(1)	(since C++20)
template< std::common_with<I> I2 >     friend constexpr strong_ordering operator<=>(         const counted_iterator& x, const counted_iterator<I2>& y );	(2)	(since C++20)

比较底层长度（即到末尾的距离）。

1) 检查底层长度是否相等。

2) 使用运算符 <=> 比较底层长度。

如果 x 和 y 不指向同一序列的元素，则行为未定义。 也就是说，必须存在某个 n 使得 std::next(x.base(), x.count() + n) 和 std::next(y.base(), y.count() + n) 指向相同的元素。

<、<=、>、>= 和 != 运算符分别从 operator<=> 和 operator== 合成。

此函数模板对于普通的非限定或限定查找是不可见的，只有当 std::counted_iterator<I> 是参数的关联类时，才能通过实参依赖查找找到它。

参数

x, y

-

迭代器适配器

返回值

1) x.count() == y.count()

2) y.count() <=> x.count()

注释

由于长度是向下计数而不是向上计数，因此底层比较表达式中 operator<=> 的参数顺序是相反的，即 y 是lhs， x 是rhs。

示例

运行此代码

#include <initializer_list>
#include <iterator>
 
int main()
{
    static constexpr auto v = {1, 2, 3, 4, 5, 6};
    constexpr std::counted_iterator<std::initializer_list<int>::iterator>
        it1{v.begin(), 5},
        it2{v.begin(), 5},
        it3{v.begin() + 1, 4},
        it4{v.begin(), 0};
    static_assert(it1 == it2);
    static_assert(it2 != it3);
    static_assert(it2 <  it3);
    static_assert(it1 <= it2);
    static_assert(it3 != std::default_sentinel);
    static_assert(it4 == std::default_sentinel);
 
//  it2 == std::counted_iterator{v.begin(), 4}; // UB: operands do not refer to
                                                // elements of the same sequence
}

参见

operator==(std::default_sentinel) (C++20)	检查到末尾的距离是否等于 ​0​ (函数模板)
operator+ (C++20)	前进迭代器 (函数模板)
operator- (C++20)	计算两个迭代器适配器之间的距离 (函数模板)