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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
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)

Range concepts
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while concat_viewviews::concat (C++26)(C++26)	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	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)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::transform_view

Member functions

transform_view::transform_view

transform_view::base

transform_view::begin

transform_view::end

transform_view::size

Deduction guides

Iterator

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)

Sentinel

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)	(since C++20)
constexpr explicit transform_view( V base, F fun );	(2)	(since C++20)

Constructs a transform_view.

1) Default constructor. Value-initializes the underlying view base_ and the transformation function fun_.

2) Move constructs the underlying view base_ from base and the transformation function fun_ from fun.

Parameters

base	-	view
fun	-	transformation function

Example

Demonstrates π approximation using serial expansion of arc tangent of 1:
atan(1) = π/4 ≈ 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...

Run this code

#include <iomanip>
#include <iostream>
#include <numbers>
#include <numeric>
#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})
    {
        auto seq = std::ranges::views::iota(0, iterations) | atan1term;
        const double accum = std::accumulate(seq.begin(), seq.end(), 0.0);
        std::cout << "π ≈ " << 4 * accum << " (iterations: " << iterations << ")\n";
    }
    std::cout << "π ≈ " << std::numbers::pi << " (std::numbers::pi)\n";
}

Possible output:

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)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3714 (P2711R1)	C++20	the multi-parameter constructor was not explicit	made explicit
P2325R3	C++20	if F is not default_initializable, the default constructor constructs a transform_view which does not contain an F	the transform_view is also not default_initializable