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std::max_element

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

Finds the greatest 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`.	(until C++20)
`std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>` is `true`.	(since C++20)

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 the first argument is less than the second. 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 greatest element in the range [first, last). If several elements in the range are equivalent to the greatest 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

max_element (1)
template<class ForwardIt> ForwardIt max_element(ForwardIt first, ForwardIt last) { if (first == last) return last; ForwardIt largest = first; ++first; for (; first != last; ++first) if (largest < first) largest = first; return largest; }
max_element (3)
template<class ForwardIt, class Compare> ForwardIt max_element(ForwardIt first, ForwardIt last, Compare comp) { if (first == last) return last; ForwardIt largest = first; ++first; for (; first != last; ++first) if (comp(largest, first)) largest = first; return largest; }

max_element (1)

template<class ForwardIt>
ForwardIt max_element(ForwardIt first, ForwardIt last)
{
    if (first == last)
        return last;
 
    ForwardIt largest = first;
    ++first;
 
    for (; first != last; ++first)
        if (*largest < *first)
            largest = first;
 
    return largest;
}

max_element (3)

template<class ForwardIt, class Compare>
ForwardIt max_element(ForwardIt first, ForwardIt last, Compare comp)
{
    if (first == last)
        return last;
 
    ForwardIt largest = first;
    ++first;
 
    for (; first != last; ++first)
        if (comp(*largest, *first))
            largest = first;
 
    return largest;
}

Example

#include <algorithm>
#include <cmath>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v {3, 1, -14, 1, 5, 9}; 
    std::vector<int>::iterator result;
 
    result = std::max_element(v.begin(), v.end());
    std::cout << "max element found at index "
              << std::distance(v.begin(), result)
              << " has value " << *result << '\n';
 
    result = std::max_element(v.begin(), v.end(), [](int a, int b)
    {
        return std::abs(a) < std::abs(b);
    });
    std::cout << "absolute max element found at index "
              << std::distance(v.begin(), result)
              << " has value " << *result << '\n';
}

Output:

max element found at index 5 has value 9
absolute max element found at index 2 has value -14

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 212	C++98	the return value was not specified if `first == last`	returns `last` in this case

min_element	returns the smallest element in a range (function template)
minmax_element (C++11)	returns the smallest and the largest elements in a range (function template)
max	returns the greater of the given values (function template)
ranges::max_element (C++20)	returns the largest element in a range (niebloid)