std::ranges::get(std::ranges::subrange)

 

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::subrange

Member functions

subrange::subrange

subrange::operator PairLike

Observers

subrange::begin

subrange::end

subrange::empty

subrange::size

Iterator operations

subrange::advance

subrange::next

subrange::prev

Deduction guides

Non-member functions

get(std::ranges::subrange)

Helper types

subrange_kind

tuple_size<std::ranges::subrange>

tuple_element<std::ranges::subrange>

 

Defined in header <ranges>
template< std::size_t N, class I, class S, ranges::subrange_kind K >     requires ((N == 0 && std::copyable<I>) || N == 1) constexpr auto get( const ranges::subrange<I, S, K>& r );	(1)	(since C++20)
template< std::size_t N, class I, class S, ranges::subrange_kind K >     requires (N < 2) constexpr auto get( ranges::subrange<I, S, K>&& r );	(2)	(since C++20)
namespace std { using ranges::get; }	(3)	(since C++20)

Provides structured binding support.

1) Obtains the iterator or sentinel from a subrange lvalue (or a const rvalue) when N == 0 or N == 1, respectively.

2) Same as (1), except that it takes a non-const subrange rvalue.

3) Overloads (1,2) are imported into namespace std, which simplifies their usage and makes every subrange with a copyable iterator a pair-like type.

Parameters

r

-

a subrange

Return value

1,2) If N is ​0​, returns r.begin(). Otherwise (N is 1), returns r.end().

Example

Run this code

#include <array>
#include <iostream>
#include <iterator>
#include <ranges>
 
int main()
{
    std::array a{1, -2, 3, -4};
 
    std::ranges::subrange sub_a{std::next(a.begin()), std::prev(a.end())};
    std::cout << *std::ranges::get<0>(sub_a) << ' '   // == *(begin(a) + 1)
              << *std::ranges::get<1>(sub_a) << '\n'; // == *(end(a) - 1)
 
    *std::get<0>(sub_a) = 42; // OK
//  *std::get<2>(sub_a) = 13; // Error: index can only be 0 or 1
}

Output:

-2 -4

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 3589	C++20	overload (1) copies begin_ if N is ​0​, but I might not model copyable	added constraints

See also

Structured binding (C++17)	binds the specified names to sub-objects or tuple elements of the initializer
get(std::tuple) (C++11)	tuple accesses specified element (function template)
get(std::pair) (C++11)	accesses an element of a pair (function template)
get(std::array) (C++11)	accesses an element of an array (function template)
get(std::variant) (C++17)	reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)
get(std::complex) (C++26)	obtains a reference to real or imaginary part from a std::complex (function template)