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 >
constexpr I
max_element( I first, S last, Comp comp = {}, Proj proj = {} );
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(1) | (since C++20) |
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>
max_element( R&& r, Comp comp = {}, Proj proj = {} );
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(2) | (since C++20) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<I, Proj>> Comp = ranges::less >
I max_element( Ep&& policy, I first, S last,
Comp comp = {}, Proj proj = {} );
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(3) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R,
class Proj = std::identity,
std::indirect_strict_weak_order
<std::projected<ranges::iterator_t<R>,
Proj>> Comp = ranges::less >
ranges::borrowed_iterator_t<R>
max_element( Ep&& policy, R&& r, Comp comp = {}, Proj proj = {} );
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(4) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
1,2) Finds the greatest element (projected by
proj) in the target range [first, last) or r, the projected values are compared using comp.3,4) Same as (1,2), but executed according to
policy.The function-like entities described on this page are algorithm function objects (informally known as 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.
Parameters
| first, last | - | the iterator-sentinel pair defining the target range |
| r | - | the target range |
| comp | - | the comparator to be applied to the (projected) elements |
| proj | - | the projection to be applied to the elements |
| policy | - | the execution policy to use |
Return value
Iterator to the greatest element in the target range.
- If there are multiple greatest elements, returns the iterator to the first one of them.
- If the target range is empty, returns its past-the-end iterator.
Complexity
Given N as ranges::distance(first, last) or ranges::distance(r):
1,2) Exactly max(N-1,0) applications of
comp, and twice as many applications of proj.3,4) 𝓞(N) applications of
comp, and twice as many applications of proj.Exceptions
3,4) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
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::next(ranges::begin(r), ranges::end(r)),
std::ref(comp), std::ref(proj));
}
};
inline constexpr max_element_fn max_element;
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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
| returns the largest element in a range (function template) | |
(C++20) |
returns the smallest element in a range (algorithm function object) |
(C++20) |
returns the smallest and the largest elements in a range (algorithm function object) |
(C++20) |
returns the greater of the given values (algorithm function object) |