std::ranges::max_element
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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| template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less > |
(1) | (since C++20) |
| template< ranges::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< |
(2) | (since C++20) |
1) Finds the greatest element in the range
[first, last). 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 pair denoting the range to examine |
| r | - | the range to examine |
| comp | - | comparison to apply to the projected elements |
| proj | - | projection to apply to the elements |
Return value
Iterator to the greatest element in the range [first, last). If several elements in the range are equivalent to the greatest element, returns the iterator to the first such element. Returns first if the range is empty.
Complexity
Exactly max(N - 1, 0) comparisons, where N = ranges::distance(first, last).
Possible implementation
struct max_element_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less> constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const { if (first == last) return last; auto largest = first; ++first; for (; first != last; ++first) if (std::invoke(comp, std::invoke(proj, *largest), std::invoke(proj, *first))) largest = first; return largest; } template<ranges::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Comp comp = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj)); } }; inline constexpr max_element_fn max_element; |
Example
Run this code
#include <algorithm> #include <cmath> #include <iostream> #include <vector> int main() { std::vector<int> v {3, 1, -14, 1, 5, 9}; namespace ranges = std::ranges; auto result = ranges::max_element(v.begin(), v.end()); std::cout << "max element at: " << ranges::distance(v.begin(), result) << '\n'; auto abs_compare = [](int a, int b) { return (std::abs(a) < std::abs(b)); }; result = ranges::max_element(v, abs_compare); std::cout << "max element (absolute) at: " << ranges::distance(v.begin(), result) << '\n'; }
Output:
max element at: 5 max element (absolute) at: 2
See also
| (C++20) |
returns the smallest element in a range (niebloid) |
| (C++20) |
returns the smallest and the largest elements in a range (niebloid) |
| (C++20) |
returns the greater of the given values (niebloid) |
| returns the largest element in a range (function template) |