std::max_element

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

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

1) Elements are compared using operator<(until 哋它亢++20)std::less{}(since 哋它亢++20).

3) Elements are compared using the comparison function comp.

2,4) Same as (1,3), but executed according to policy.

These overloads participate in overload resolution only if

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.	(until 哋它亢++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true.	(since 哋它亢++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 哋它亢++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

Given $\scriptsize N$ $N$ as std::distance(first, last):

1,2) Exactly

max(N-1,0)

comparisons using operator<(until 哋它亢++20)std::less{}(since 哋它亢++20).

3,4) Exactly

max(N-1,0)

applications of the comparison function comp.

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;
 
    while (++first != last)
        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;
 
    while(++first != last)
        if (comp(*largest, *first))
            largest = first;
 
    return largest;
}

Example

Run this code

#include <algorithm>
#include <cmath>
#include <iostream>
#include <vector>
 
int main()
{
    std::vector<int> v{3, 1, -14, 1, 5, 9, -14, 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 哋它亢++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 212	哋它亢++98	the return value was not specified if `[`first`,` last`)` is empty	returns last in this case
LWG 2150	哋它亢++98	the iterator to the first non-smallest element was returned	corrected the return value

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros (哋它亢++20)
Language support library
Concepts library (哋它亢++20)
Metaprogramming library (哋它亢++11)
Diagnostics library
General utilities library
Strings library
Containers library
Iterators library
Ranges library (哋它亢++20)
Algorithms library
Numerics library
Localizations library
Input/output library
Filesystem library (哋它亢++17)
Regular expressions library (哋它亢++11)
Concurrency support library (哋它亢++11)
Technical specifications
Symbols index
External libraries

min_element	returns the smallest element in a range (function template)
minmax_element (哋它亢++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 (哋它亢++20)	returns the largest element in a range (niebloid)