NAME¶

std::ranges::max_element - std::ranges::max_element

Synopsis¶

Defined in header <algorithm>
Call signature
template< std::forward_iterator I, std::sentinel_for<I> S, class Proj =
std::identity,

std::indirect_strict_weak_order<std::projected<I, Proj>> Comp (1) (since
= ranges::less > C++20)
constexpr I

max_element( I first, S last, Comp comp = {}, Proj proj = {} );
template< ranges::forward_range R, class Proj = std::identity,

std::indirect_strict_weak_order<
std::projected<ranges::iterator_t<R>, Proj>> Comp = (2) (since
ranges::less > C++20)
constexpr ranges::borrowed_iterator_t<R>

max_element( R&& r, Comp comp = {}, Proj proj = {} );

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 last if the range is empty (i.e. if first == last).

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;
while (++first != last)
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>

int main()
{
namespace ranges = std::ranges;

const auto v = {3, 1, -14, 1, 5, 9, -14, 9};

auto result = ranges::max_element(v.begin(), v.end());
std::cout << "Max element at pos " << 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 << "Absolute max element at pos "
<< ranges::distance(v.begin(), result) << '\n';
}

Output:¶

Max element at pos 5
Absolute max element at pos 2

See also¶

ranges::min_element returns the smallest element in a range
(C++20) (niebloid)
ranges::minmax_element returns the smallest and the largest elements in a range
(C++20) (niebloid)
ranges::max returns the greater of the given values
(C++20) (niebloid)
max_element returns the largest element in a range
(function template)