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std::ranges::min_element

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 = ranges::less >
constexpr I
    min_element( I first, S last, Comp comp = {}, Proj proj = {} );
 (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>
    min_element( R&& r, Comp comp = {}, Proj proj = {} );
 (2) (since C++20)
1) Finds the smallest 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:

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 smallest element in the range [first, last). If several elements in the range are equivalent to the smallest 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 min_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 smallest = first;
        ++first;
        for (; first != last; ++first)
            if (!std::invoke(comp, std::invoke(proj, *smallest), std::invoke(proj, *first)))
                smallest = first;
        return smallest;
    }
 
    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 min_element_fn min_element;

Example

#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::min_element(v.begin(), v.end());
    std::cout << "min element at [" << ranges::distance(v.begin(), result)
              << "]\n";
 
    auto abs_compare = [](int a, int b) { return (std::abs(a) < std::abs(b)); };
    result = ranges::min_element(v, abs_compare);
    std::cout << "|min| element at [" << ranges::distance(v.begin(), result)
              << "]\n";
}

Output:

min element at [2]
|min| element at [1]

See also

(C++20)
returns the largest 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 smallest element in a range
(function template)

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https://en.cppreference.com/w/cpp/algorithm/ranges/min_element