std::ranges::subrange

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

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)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range primitives
iterator_tsentinel_t	range_size_trange_difference_t	range_value_t	range_reference_trange_rvalue_reference_t
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
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
Views
view_interface	subrange
Semiregular wrapper
Factories
empty_viewviews::empty	single_viewviews::single	iota_viewviews::iota	views::counted
Adaptors
views::all_tviews::all join_viewviews::join take_viewviews::take basic_istream_viewistream_view	ref_view                                split_viewviews::split take_while_viewviews::take_while elements_viewviews::elements	common_viewviews::common transform_viewviews::transform drop_viewviews::drop keys_viewviews::keys	reverse_viewviews::reverse filter_viewviews::filter drop_while_viewviews::drop_while values_viewviews::values

 

Defined in header <ranges>
template<   std::input_or_output_iterator I,   std::sentinel_for<I> S = I,   ranges::subrange_kind K = std::sized_sentinel_for<S, I> ?     ranges::subrange_kind::sized : ranges::subrange_kind::unsized >   requires (K == ranges::subrange_kind::sized || !std::sized_sentinel_for<S, I>) class subrange : public ranges::view_interface<subrange<I, S, K>>		(since C++20)

The subrange class template combines together an iterator and a sentinel into a single view.

Additionally, the subrange is a sized_range whenever the final template parameter is subrange_kind​::​sized (which happens when sized_sentinel_for<S, I> is satisfied or when size is passed explicitly as a constructor argument)

Helper templates

template<std::input_or_output_iterator I, std::sentinel_for<I> S          ranges::subrange_kind K> inline constexpr bool enable_borrowed_range<ranges::subrange<I, S, K>> = true;

This specialization of std::ranges::enable_borrowed_range makes subrange satisfy borrowed_range.

Example

Run this code

#include <iostream>
#include <map>
#include <ranges>
#include <string_view>
 
template <class V> void mutate(V& v) { v += 'A' - 'a'; }
 
template <class K, class V>
void mutate_map_values(std::multimap<K, V>& m, K k) {
    auto iter_pair = m.equal_range(k);
    for (auto& [_, v] : std::ranges::subrange(iter_pair.first, iter_pair.second)) {
        mutate(v);
    }
}
 
int main()
{
    auto print = [](std::string_view rem, auto const& mm) {
        std::cout << rem << "{ ";
        for (const auto& [k, v] : mm) std::cout << "{" << k << ",'" << v << "'} ";
        std::cout << "}\n";
    };
 
    std::multimap<int,char> mm{ {4,'a'}, {3,'-'}, {4,'b'}, {5,'-'}, {4,'c'} };
    print("Before: ", mm);
    mutate_map_values(mm, 4);
    print("After:  ", mm);
}

Output:

Before: { {3,'-'} {4,'a'} {4,'b'} {4,'c'} {5,'-'} }
After:  { {3,'-'} {4,'A'} {4,'B'} {4,'C'} {5,'-'} }