# std::max_element

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< cpp‎ | algorithm

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

### 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

First version

    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;
    }

Second version

    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

Run this code

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

    static bool abs_compare(int a, int b)
    {
        return (std::abs(a) < std::abs(b));
    }

    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 at: " << std::distance(v.begin(), result) << '\n';

        result = std::max_element(v.begin(), v.end(), abs_compare);
        std::cout << "max element (absolute) at: " << std::distance(v.begin(), result);
    }

Output:

    max element at: 5
    max element (absolute) at: 2

### See also

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)

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