std::ranges::upper_bound(3)

NAME
std::ranges::upper_bound - std::ranges::upper_bound

Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::forward_iterator I, std::sentinel_for<I> S,
             class T, class Proj = std::identity, (since
             std::indirect_strict_weak_order C++20)
                 <const T*, std::projected<I, Proj>> Comp = (until
   ranges::less > C++26)
   constexpr I upper_bound( I first, S last, const T& value,
                        Comp comp = {}, Proj proj = {} );
   template< std::forward_iterator I, std::sentinel_for<I> S,
             class Proj = std::identity,
             class T = std::projected_value_t<I, Proj>,
             std::indirect_strict_weak_order (since
                 <const T*, std::projected<I, Proj>> Comp = C++26)
   ranges::less >
   constexpr I upper_bound( I first, S last, const T& value,
                        Comp comp = {}, Proj proj = {} );
   template< ranges::forward_range R,
             class T, class Proj = std::identity,
             std::indirect_strict_weak_order (1)
                 <const T*, (since
   std::projected<ranges::iterator_t<R>, C++20)
                        Proj>> Comp = (until
   ranges::less > C++26)
   constexpr ranges::borrowed_iterator_t<R>
       upper_bound( R&& r, const T& value, Comp comp = {}, Proj
   proj = {} );
   template< ranges::forward_range R, (2)
             class Proj = std::identity,
             class T =
   std::projected_value_t<ranges::iterator_t<R>, Proj>,
             std::indirect_strict_weak_order
                 <const T*, (since
   std::projected<ranges::iterator_t<R>, C++26)
                        Proj>> Comp =
   ranges::less >
   constexpr ranges::borrowed_iterator_t<R>
       upper_bound( R&& r, const T& value, Comp comp = {}, Proj
   proj = {} );
   1) Returns an iterator pointing to the first element in the range [first, last) that
   is greater than value, or last if no such element is found. The range [first, last)
   must be partitioned with respect to the expression or !comp(value, element), i.e.,
   all elements for which the expression is true must precede all elements for which
   the expression is false. A fully-sorted range meets this criterion.
   2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as
   first and ranges::end(r) as last.
   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
   first, last - iterator-sentinel defining the partially-ordered range to examine
   r - the partially-ordered range to examine
   value - value to compare the elements to
   pred - predicate to apply to the projected elements
   proj - projection to apply to the elements

Return value
   Iterator pointing to the first element that is greater than value, or last if no
   such element is found.

Complexity
   The number of comparisons and applications of the projection performed are
   logarithmic in the distance between first and last (at most log
   2(last - first) + O(1) comparisons and applications of the projection). However, for
   an iterator that does not model random_access_iterator, the number of iterator
   increments is linear.

Possible implementation
   struct upper_bound_fn
   {
       template<std::forward_iterator I, std::sentinel_for<I> S,
                class Proj = std::identity, class T = std::projected_value_t<I, Proj>,
                std::indirect_strict_weak_order
                    <const T*, std::projected<I, Proj>> Comp = ranges::less>
       constexpr I operator()(I first, S last, const T& value,
                        Comp comp = {}, Proj proj = {}) const
       {
           I it;
           std::iter_difference_t<I> count, step;
           count = ranges::distance(first, last);
           while (count > 0)
           {
               it = first;
               step = count / 2;
               ranges::advance(it, step, last);
               if (!comp(value, std::invoke(proj, *it)))
               {
                   first = ++it;
                   count -= step + 1;
               }
               else
                   count = step;
           }
           return first;
       }
       template<ranges::forward_range R, class Proj = std::identity,
                class T = std::projected_value_t<ranges::iterator_t<R>, Proj>,
                std::indirect_strict_weak_order
                    <const T*, std::projected<ranges::iterator_t<R>,
                        Proj>> Comp = ranges::less>
       constexpr ranges::borrowed_iterator_t<R>
           operator()(R&& r, const T& value, Comp comp = {}, Proj proj = {}) const
       {
           return (*this)(ranges::begin(r), ranges::end(r), value,
                        std::ref(comp), std::ref(proj));
       }
   };
   inline constexpr upper_bound_fn upper_bound;

Notes
             Feature-test macro Value Std Feature
   __cpp_lib_algorithm_default_value_type 202403 (C++26) List-initialization for
                        algorithms (1,2)

Example
// Run this code
 #include <algorithm>
 #include <cassert>
 #include <complex>
 #include <iostream>
 #include <iterator>
 #include <vector>
 int main()
 {
     namespace ranges = std::ranges;
     std::vector<int> data{1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6};
     {
         auto lower = ranges::lower_bound(data.begin(), data.end(), 4);
         auto upper = ranges::upper_bound(data.begin(), data.end(), 4);
         ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " "));
         std::cout << '\n';
     }
     {
         auto lower = ranges::lower_bound(data, 3);
         auto upper = ranges::upper_bound(data, 3);
         ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " "));
         std::cout << '\n';
     }
     using CD = std::complex<double>;
     std::vector<CD> nums{{1, 0}, {2, 2}, {2, 1}, {3, 0}, {3, 1}};
     auto cmpz = [](CD x, CD y) { return x.real() < y.real(); };
     #ifdef __cpp_lib_algorithm_default_value_type
         auto it = ranges::upper_bound(nums, {2, 0}, cmpz);
     #else
         auto it = ranges::upper_bound(nums, CD{2, 0}, cmpz);
     #endif
     assert((*it == CD{3, 0}));
 }

Output:
 4 4 4
 3 3 3 3

See also
   ranges::equal_range returns range of elements matching a specific key
   (C++20) (niebloid)
   ranges::lower_bound returns an iterator to the first element not less than the given
   (C++20) value
                       (niebloid)
   ranges::partition divides a range of elements into two groups
   (C++20) (niebloid)
                       returns an iterator to the first element greater than a certain
   upper_bound value
                       (function template)