# std::ranges::min_element

From cppreference.com
< cpp‎ | algorithm‎ | ranges

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:

- 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 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

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::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

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

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