# std::ranges::includes

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< cpp‎ | algorithm‎ | ranges

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 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.

In practice, they may be implemented as function objects, or with special compiler extensions.

### 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 \(\scriptsize 2 \cdot (N_1+N_2-1)\)2·(N1+N2-1) comparisons, where \(\scriptsize N_1\)N1 is ranges::distance(r1) and \(\scriptsize N_2\)N2 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

### See also

ranges::set_difference (C++20) | computes the difference between two sets (niebloid)
ranges::search (C++20) | searches for a range of elements (niebloid)
ranges::contains ranges::contains_subrange (C++23)(C++23) | checks if the range contains the given element or subrange (niebloid)
includes | returns true if one sequence is a subsequence of another (function template)

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