std::min_element

Defined in header `<algorithm>`
	(1)
template< class ForwardIt > ForwardIt min_element( ForwardIt first, ForwardIt last );			(until C++17)
template< class ForwardIt > constexpr ForwardIt min_element( ForwardIt first, ForwardIt last );			(since C++17)
template< class ExecutionPolicy, class ForwardIt > ForwardIt min_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );		(2)	(since C++17)
		(3)
template< class ForwardIt, class Compare > ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );				(until C++17)
template< class ForwardIt, class Compare > constexpr ForwardIt min_element( ForwardIt first, ForwardIt last, Compare comp );				(since C++17)
template< class ExecutionPolicy, class ForwardIt, class Compare > ForwardIt min_element( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Compare comp );			(4)	(since C++17)

Finds the smallest element in the range [first, last).

1) Elements are compared using operator<.

3) Elements are compared using the given binary comparison function comp.

2,4) Same as (1,3), but executed according to policy. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last	-	forward iterators defining the range to examine
policy	-	the execution policy to use. See execution policy for details.
comp	-	comparison function object (i.e. an object that satisfies the requirements of Compare) which returns true if `a` is less than `b`. The signature of the comparison function should be equivalent to the following: bool cmp(const Type1 &a, const Type2 &b); The signature does not need to have const &, but the function object must not modify the objects passed to it. The types Type1 and Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them.
Type requirements
- `ForwardIt` must meet the requirements of ForwardIterator.

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 last if the range is empty.

Complexity

Exactly $max(N-1,0)$ comparisons, where N = std::distance(first, last).

Exceptions

The overloads with a template parameter named ExecutionPolicy report errors as follows:

If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the three standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation

First version

template<class ForwardIt>
ForwardIt min_element(ForwardIt first, ForwardIt last)
{
    if (first == last) return last;

    ForwardIt smallest = first;
    ++first;
    for (; first != last; ++first) {
        if (*first < *smallest) {
            smallest = first;
        }
    }
    return smallest;
}

Second version

template<class ForwardIt, class Compare>
ForwardIt min_element(ForwardIt first, ForwardIt last, 
                            Compare comp)
{
    if (first == last) return last;

    ForwardIt smallest = first;
    ++first;
    for (; first != last; ++first) {
        if (comp(*first, *smallest)) {
            smallest = first;
        }
    }
    return smallest;
}

Example

Run this code

#include <algorithm>
#include <iostream>
#include <vector>

int main()
{
    std::vector<int> v{3, 1, 4, 1, 5, 9};

    std::vector<int>::iterator result = std::min_element(std::begin(v), std::end(v));
    std::cout << "min element at: " << std::distance(std::begin(v), result);
}

Output:

min element at: 1

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

max_element	returns the largest element in a range (function template)
minmax_element (C++11)	returns the smallest and the largest elements in a range (function template)
min	returns the smaller of the given values (function template)