Difference between revisions of "cpp/algorithm/ranges/upper bound"
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===Notes=== | ===Notes=== | ||
| − | {{feature test macro| | + | {{feature test macro|__cpp_lib_algorithm_default_value_type|value=202403|std=C++26|[[cpp/language/list initialization|List-initialization]] for algorithms {{vl|1,2}}}} |
===Example=== | ===Example=== | ||
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std::vector<CD> nums{<!---->{1, 0}, {2, 2}, {2, 1}, {3, 0}, {3, 1}<!---->}; | 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(); }; | auto cmpz = [](CD x, CD y) { return x.real() < y.real(); }; | ||
| − | #ifdef | + | #ifdef __cpp_lib_algorithm_default_value_type |
auto it = ranges::upper_bound(nums, {2, 0}, cmpz); | auto it = ranges::upper_bound(nums, {2, 0}, cmpz); | ||
#else | #else | ||
Latest revision as of 21:34, 20 May 2024
| Defined in header <algorithm>
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| Call signature |
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| (1) | ||
template< std::forward_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity, |
(since C++20) (until C++26) |
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| template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, |
(since C++26) | |
| (2) | ||
| template< ranges::forward_range R, class T, class Proj = std::identity, |
(since C++20) (until C++26) |
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| template< ranges::forward_range R, class Proj = std::identity, |
(since C++26) | |
[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.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.
Contents |
[edit] 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 |
[edit] Return value
Iterator pointing to the first element that is greater than value, or last if no such element is found.
[edit] Complexity
The number of comparisons and applications of the projection performed are logarithmic in the distance between first and last (at most log2(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.
[edit] 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; |
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 | (C++26) | List-initialization for algorithms (1,2) |
[edit] Example
#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
[edit] See also
| (C++20) |
returns range of elements matching a specific key (niebloid) |
| (C++20) |
returns an iterator to the first element not less than the given value (niebloid) |
| (C++20) |
divides a range of elements into two groups (niebloid) |
| returns an iterator to the first element greater than a certain value (function template) |
