std::ranges::iota_view<W, Bound>::size

 

C++

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独立和宿主式

语言

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标准库头文件

具名要求

特性测试宏 (C++20)

语言支持库

概念库 (C++20)

诊断库

内存管理库

元编程库 (C++11)

通用工具库

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文件系统库 (C++17)

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技术规范

符号索引

外部库

 

范围库

范围访问 begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata reserve_hint (C++26)   empty

范围转换 std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

悬垂迭代器处理 dangling borrowed_iterator_t borrowed_subrange_t

范围基元
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

范围概念
range borrowed_range    common_range	sized_range viewable_range    view	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	approximately_sized_range (C++26) constant_range (C++23)

视图
view_interface	subrange

范围工厂
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

范围适配器
views::all_tviews::all as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while common_viewviews::common views::counted to_input_viewviews::to_input (C++26)(C++26)	ref_view drop_viewviews::drop drop_while_viewviews::drop_while lazy_split_viewviews::lazy_split split_viewviews::split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   concat_viewviews::concat (C++26)(C++26) cache_latest_viewviews::cache_latest (C++26)(C++26)	owning_view reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

范围生成器 std::generator (C++23)

范围适配器闭包对象 range_adaptor_closure (C++23)

范围适配器对象

辅助项
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::iota_view

成员函数

iota_view::iota_view

iota_view::begin

iota_view::end

iota_view::empty

iota_view::size

推导指引

嵌套类

Iterator

辅助概念

decrementable

advanceable

成员类型

成员函数

iota_view::iterator::iterator

iota_view::iterator::operator*

iota_view::iterator::operator[]

iota_view::iterator::operator++ iota_view::iterator::operator++(int)

iota_view::iterator::operator-- iota_view::iterator::operator--(int)

iota_view::iterator::operator+=

iota_view::iterator::operator-=

非成员函数

operator==(iota_view::iterator) operator<(iota_view::iterator) operator>(iota_view::iterator) operator<=(iota_view::iterator) operator>=(iota_view::iterator) operator<=>(iota_view::iterator)

operator+(iota_view::iterator)

operator-(iota_view::iterator)

Sentinel

成员函数

iota_view::sentinel::sentinel

非成员函数

operator==(iota_view::iterator,iota_view::sentinel)

operator-(iota_view::iterator,iota_view::sentinel)

 

constexpr auto size() const     requires (std::same_as<W, Bound> && /*advanceable*/<W>) ||              (/*is-integer-like*/<W> && /*is-integer-like*/<Bound>) ||              std::sized_sentinel_for<Bound, W>;		(自 C++20 起)

若视图有界，则返回视图的大小。

关于 /*advanceable*/ 和 /*is-integer-like*/ 的定义，见 advanceable 和 is-integer-like。

返回值

若 W 和 Bound 中有任何一个不是类整数类型，则返回 to-unsigned-like (bound_ - value_ )。

否则，返回 (value_ < 0) ?
    (
        (bound_ < 0) ?
            to-unsigned-like (-value_ ) - to-unsigned-like (-bound_ ) :
            to-unsigned-like (bound_ ) + to-unsigned-like (-value_ )
    ) :
    to-unsigned-like (bound_ ) - to-unsigned-like (value_ ) 。

示例

运行此代码

#include <cassert>
#include <ranges>
 
int main()
{
    unsigned initial_value{1}, bound{5};
    auto i{std::views::iota(initial_value, bound)};
    assert(i.size() == bound - initial_value and i.size() == 4);
 
    auto u{std::views::iota(8)};
    // assert(u.size()); // Error: size() is not present since “u” is unbounded
}

缺陷报告

下列行为变更缺陷报告被追溯应用于先前发布的 C++ 标准。

DR	应用于	已发布行为	正确行为
LWG 3610	C++20	size 可能拒绝整数类类型	如果可能则接受

参见

ranges::size (C++20)	返回等于范围大小的整数 (定制点对象)
ranges::ssize (C++20)	返回等于范围大小的有符号整数 (定制点对象)