std::ranges::views::transform, std::ranges::transform_view

 

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特性测试宏 (C++20)

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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

范围原语
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::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)

 

定义于头文件 <ranges>
	(1)
template< ranges::input_range V,           std::copy_constructible F >     requires ranges::view<V> &&              std::is_object_v<F> &&              std::regular_invocable<F&, ranges::range_reference_t<V>> &&              /* invoke_result_t<F&, range_reference_t<V>>& is a valid type */ class transform_view     :: public ranges::view_interface<transform_view<V, F>>			(since C++20) (until C++23)
template< ranges::input_range V,           std::move_constructible F >     requires ranges::view<V> &&              std::is_object_v<F> &&              std::regular_invocable<F&, ranges::range_reference_t<V>> &&              /* invoke_result_t<F&, range_reference_t<V>>& is a valid type */ class transform_view     :: public ranges::view_interface<transform_view<V, F>>			(since C++23)
namespace views {     inline constexpr /*unspecified*/ transform = /*unspecified*/; }		(2)	(since C++20)
调用签名
template< ranges::viewable_range R, class F >     requires /* see below */ constexpr ranges::view auto transform( R&& r, F&& fun );			(since C++20)
template< class F > constexpr /*range adaptor closure*/ transform( F&& fun );			(since C++20)

1) 范围适配器，表示将变换函数应用于每个元素后的底层序列的 view。

2) RangeAdaptorObject。 表达式 views::transform(e, f) 表达式等价于 transform_view(e, f)，对于任何合适的子表达式 e 和 f。

当底层视图 V 建模相应的概念时，transform_view 建模概念 random_access_range、 bidirectional_range、 forward_range、 input_range、 common_range 和 sized_range。

数据成员

成员	描述
V base_ (private)	底层视图 (仅用于演示的成员对象*)
copyable-box<F>(until C++23)movable-box<F>(since C++23) fun_ (private)	底层函数对象 (仅用于演示的成员对象*)

成员函数

(构造函数)	构造一个 transform_view (public member function)
base	返回底层（适配的）视图的副本 (public member function)
begin	返回指向开始的迭代器 (public member function)
end	返回指向末尾的迭代器或哨位 (public member function)
size	仅当底层（适配的）范围满足 sized_range 时提供，返回元素数量 (public member function)
继承自 std::ranges::view_interface
empty	仅当派生视图满足 sized_range 或 forward_range 时提供，返回派生视图是否为空 (public member function of std::ranges::view_interface<D>)
cbegin (C++23)	返回指向范围开始的常量迭代器 (public member function of std::ranges::view_interface<D>)
cend (C++23)	返回范围的常量迭代器的哨位 (public member function of std::ranges::view_interface<D>)
operator bool	仅当 ranges::empty 适用于派生视图时提供，返回派生视图是否非空 (public member function of std::ranges::view_interface<D>)
front	仅当派生视图满足 forward_range 时提供，返回派生视图中的第一个元素 (public member function of std::ranges::view_interface<D>)
back	仅当派生视图满足 bidirectional_range 和 common_range 时提供，返回派生视图中的最后一个元素 (public member function of std::ranges::view_interface<D>)
operator[]	仅当派生视图满足 random_access_range 时提供，返回派生视图中的第 nth 个元素 (public member function of std::ranges::view_interface<D>)

嵌套类

iterator	迭代器类型 (仅用于演示的成员类模板*)
sentinel	哨位类型 (仅用于演示的成员类模板*)

示例

运行此代码

#include <algorithm>
#include <cstdio>
#include <iterator>
#include <ranges>
#include <string>
 
char rot13a(const char x, const char a)
{
    return a + (x - a + 13) % 26;
}
 
char rot13(const char x)
{
    if ('Z' >= x and x >= 'A')
        return rot13a(x, 'A');
 
    if ('z' >= x and x >= 'a')
        return rot13a(x, 'a');
 
    return x;
}
 
int main()
{
    auto show = [](const unsigned char x) { std::putchar(x); };
 
    std::string in{"cppreference.cn\n"};
    std::ranges::for_each(in, show);
    std::ranges::for_each(in | std::views::transform(rot13), show);
 
    std::string out;
    std::ranges::copy(std::views::transform(in, rot13), std::back_inserter(out));
    std::ranges::for_each(out, show);
    std::ranges::for_each(out | std::views::transform(rot13), show);
}

输出

cppreference.cn
pccersrerapr.pbz
pccersrerapr.pbz
cppreference.cn

参见

ranges::transform (C++20)

将函数应用于元素范围 (algorithm function object)