std::ranges::transform_view<V,F>::transform_view

 

C++

语言

标准库头文件

自立与有宿主实现

具名要求

语言支持库

概念库 (C++20)

诊断库

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)

原子操作库 (C++11)

线程支持库 (C++11)

技术规范

 

范围库

范围访问
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
范围原语
iterator_tsentinel_t	range_size_trange_difference_t	range_reference_trange_rvalue_reference_t	range_value_t
悬垂迭代器处理
dangling	borrowed_iterator_t	borrowed_subrange_t
范围概念
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
视图
view_interface	subrange
范围工厂
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	basic_istream_viewviews::istream
适配器
views::all_tviews::all ref_view owning_view common_viewviews::common reverse_viewviews::reverse views::counted zip_viewviews::zip (C++23)(C++23)	take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while zip_transform_viewviews::zip_transform (C++23)(C++23)	elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform adjacent_viewviews::adjacent (C++23)(C++23)	filter_viewviews::filter join_viewviews::join split_viewviews::split lazy_split_viewviews::lazy_split adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)
范围适配器对象
范围适配器闭包对象
辅助项
copyable-box	simple-view

 

std::ranges::transform_view

成员函数

transform_view::transform_view

transform_view::base

transform_view::begin

transform_view::end

transform_view::size

推导指引

迭代器

transform_view::iterator::iterator

transform_view::iterator::base

transform_view::iterator::operator*

transform_view::iterator::operator[]

transform_view::iterator::operator++ transform_view::iterator::operator++(int) transform_view::iterator::operator-- transform_view::iterator::operator--(int) transform_view::iterator::operator+= transform_view::iterator::operator-=

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

operator+(transform_view::iterator) operator-(transform_view::iterator)

iter_move(transform_view::iterator)

哨位

transform_view::sentinel::sentinel

transform_view::sentinel::base

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

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

 

transform_view() requires std::default_initializable<V> &&                           std::default_initializable<F> = default;	(1)	(C++20 起)
constexpr transform_view( V base, F fun );	(2)	(C++20 起)

构造 transform_view 。

1) 默认构造函数。值初始化底层视图与变换函数。

2) 从 base 移动构造视图并从 fun 移动构造变换函数。

参数

base	-	视图
fun	-	变换函数

示例

演示使用 1 的反正切的级数展开的 π 近似：
atan(1) = π/4 ~ 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...

运行此代码

#include <iomanip>
#include <iostream>
#include <numbers>
#include <ranges>
 
int main()
{
    std::cout << std::setprecision(15) << std::fixed;
    auto atan1term = std::ranges::views::transform(
        [](int n) { return ((n % 2) ? -1 : 1) * 1.0 / (2 * n + 1); }
    );
    for (const int iterations : {1, 2, 3, 4, 5, 10, 100, 1000, 1'000'000}) {
        double accum{0.0};
        for (double term : std::ranges::views::iota(0, iterations) | atan1term) {
            accum += term;
        }
        std::cout << "π ~ " << 4 * accum << " (iterations: " << iterations << ")\n";
    }
    std::cout << "π ~ " << std::numbers::pi << " (std::numbers::pi)\n";
}

可能的输出：

π ~ 4.000000000000000 (iterations: 1)
π ~ 2.666666666666667 (iterations: 2)
π ~ 3.466666666666667 (iterations: 3)
π ~ 2.895238095238096 (iterations: 4)
π ~ 3.339682539682540 (iterations: 5)
π ~ 3.041839618929403 (iterations: 10)
π ~ 3.131592903558554 (iterations: 100)
π ~ 3.140592653839794 (iterations: 1000)
π ~ 3.141591653589774 (iterations: 1000000)
π ~ 3.141592653589793 (std::numbers::pi)

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。

DR	应用于	出版时的行为	正确行为
P2325R3	C++20	若 F 非 default_initializable ，则默认构造函数构造不含 F 的 transform_view	transform_view 亦非 default_initializable