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);` While the signature does not need to have `const &`, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) `Type1` and `Type2` regardless of value category (thus, `Type1 &` is not allowed, nor is `Type1` unless for `Type1` a move is equivalent to a copy (since C++11)). 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 LegacyForwardIterator.

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 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; }

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

#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

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)