std::ranges:: includes

From cppreference.com

Defined in header `<algorithm>`
Call signature
template < std:: input_iterator I1, std:: sentinel_for < I1 > S1, std:: input_iterator I2, std:: sentinel_for < I2 > S2, class Proj1 = std:: identity , class Proj2 = std:: identity , std:: indirect_strict_weak_order < std :: projected < I1, Proj1 > , std :: projected < I2, Proj2 >> Comp = ranges:: less > constexpr bool includes ( I1 first1, S1 last1, I2 first2, S2 last2, Comp comp = { } , Proj1 proj1 = { } , Proj2 proj2 = { } )	(1)	(since C++20)
template < ranges:: input_range R1, ranges:: input_range R2, class Proj1 = std:: identity , class Proj2 = std:: identity , std:: indirect_strict_weak_order < std :: projected < ranges:: iterator_t < R1 > , Proj1 > , std :: projected < ranges:: iterator_t < R2 > , Proj2 >> Comp = ranges:: less > constexpr bool includes ( R1 && r1, R2 && r2, Comp comp = { } , Proj1 proj1 = { } , Proj2 proj2 = { } )	(2)	(since C++20)

1) Returns true if the projections of the sorted range

first2

last2

is a subsequence of the projections of the sorted range

first1

last1

2) Same as (1) , but uses r1 and r2 as the source ranges, as if by using ranges:: begin ( r1 ) and ranges:: begin ( r2 ) as first1 and first2 respectively, and ranges:: end ( r1 ) and ranges:: end ( r2 ) as last1 and last2 respectively.

Both ranges must be sorted with the given comparison function comp . A subsequence need not be contiguous.

The function-like entities described on this page are algorithm function objects (informally known as niebloids ), that is:

Explicit template argument lists cannot be specified when calling any of them.
None of them are visible to argument-dependent lookup .
When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

Parameters

first1, last1	-	the sorted range of elements to examine
r1	-	the sorted range of elements to examine
first2, last2	-	the sorted range of elements to search for
r2	-	the sorted range of elements to search for
comp	-	comparison function to apply to the projected elements
proj1	-	projection to apply to the elements in the first range
proj2	-	projection to apply to the elements in the second range

Return value

true if [ first2 , last2 ) is a subsequence of [ first1 , last1 ) ; otherwise false .

Complexity

At most $2\cdot(N 1 +N 2 -1)$ comparisons, where $\scriptsize N_1$ $N 1$ is ranges:: distance ( r1 ) and $\scriptsize N_2$ $N 2$ is ranges:: distance ( r2 ) .

Possible implementation

struct includes_fn
{
    template<std::input_iterator I1, std::sentinel_for<I1> S1,
             std::input_iterator I2, std::sentinel_for<I2> S2,
             class Proj1 = std::identity, class Proj2 = std::identity,
             std::indirect_strict_weak_order<
                 std::projected<I1, Proj1>,
                 std::projected<I2, Proj2>> Comp = ranges::less>
    constexpr bool operator()(I1 first1, S1 last1, I2 first2, S2 last2,
                              Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        for (; first2 != last2; ++first1)
        {
            if (first1 == last1 || comp(*first2, *first1))
                return false;
            if (!comp(*first1, *first2))
                ++first2;
        }
        return true;
    }
 
    template<ranges::input_range R1, ranges::input_range R2,
             class Proj1 = std::identity, class Proj2 = std::identity,
             std::indirect_strict_weak_order<
                 std::projected<ranges::iterator_t<R1>, Proj1>,
                 std::projected<ranges::iterator_t<R2>, Proj2>> Comp = ranges::less>
    constexpr bool operator()(R1&& r1, R2&& r2, Comp comp = {},
                              Proj1 proj1 = {}, Proj2 proj2 = {}) const
    {
        return (*this)(ranges::begin(r1), ranges::end(r1),
                       ranges::begin(r2), ranges::end(r2),
                       std::ref(comp), std::ref(proj1), std::ref(proj2));
    }
};
 
inline constexpr auto includes = includes_fn {};

Example

Run this code

#include <algorithm>
#include <cctype>
#include <initializer_list>
#include <iomanip>
#include <iostream>
#include <locale>
#include <string>
 
template<class T>
std::ostream& operator<<(std::ostream& os, std::initializer_list<T> const& list)
{
    for (os << "{ "; auto const& elem : list)
        os << elem << ' ';
    return os << "} ";
}
 
struct true_false : std::numpunct<char>
{
    std::string do_truename() const { return "? Yes\n"; }
    std::string do_falsename() const { return "? No\n"; }
};
 
int main()
{
    std::cout.imbue(std::locale(std::cout.getloc(), new true_false));
 
    auto ignore_case = [](char a, char b) { return std::tolower(a) < std::tolower(b); };
 
    const auto
        a = {'a', 'b', 'c'},
        b = {'a', 'c'},
        c = {'a', 'a', 'b'},
        d = {'g'},
        e = {'a', 'c', 'g'},
        f = {'A', 'B', 'C'},
        z = {'a', 'b', 'c', 'f', 'h', 'x'};
 
    std::cout
        << z << "includes\n" << std::boolalpha
        << a << std::ranges::includes(z.begin(), z.end(), a.begin(), a.end())
        << b << std::ranges::includes(z, b)
        << c << std::ranges::includes(z, c)
        << d << std::ranges::includes(z, d)
        << e << std::ranges::includes(z, e)
        << f << std::ranges::includes(z, f, ignore_case);
}

Output:

{ a b c f h x } includes
{ a b c } ? Yes
{ a c } ? Yes
{ a a b } ? No
{ g } ? No
{ a c g } ? No
{ A B C } ? Yes

Compiler support
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Language
Standard library
Standard library headers
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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
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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::set_difference (C++20)	computes the difference between two sets (algorithm function object)
ranges::search (C++20)	searches for the first occurrence of a range of elements (algorithm function object)
ranges::contains ranges::contains_subrange (C++23) (C++23)	checks if the range contains the given element or subrange (algorithm function object)
includes	returns true if one sequence is a subsequence of another (function template)