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# std::max_element

From cppreference.com
< 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 cmp); |  | (until C++17)
template< class ForwardIt, class Compare > constexpr ForwardIt max_element(ForwardIt first, ForwardIt last, Compare cmp); |  | (since C++17)
template< class ExecutionPolicy, class ForwardIt, class Compare > ForwardIt max_element( ExecutionPolicy&& policy,ForwardIt first, ForwardIt last, Compare cmp); | (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

### [edit] Parameters

first, last | - | forward iterators defining the range to examine
policy | - | the execution policy to use. See execution policy for details.
cmp | - | 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); 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`.

### [edit] 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.

### [edit] Complexity

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

### [edit] 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.

### [edit] 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 cmp)
    {
        if (first == last) {
            return last;
        }
        ForwardIt largest = first;
        ++first;
        for (; first != last; ++first) {
            if (cmp(*largest, *first)) {
                largest = first;
            }
        }
        return largest;
    }

### [edit] 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

### [edit] See also

min_element | returns the smallest element in a range (function template) [edit]
minmax_element (C++11) | returns the smallest and the largest elements in a range (function template) [edit]
max | returns the greater of the given values (function template) [edit]

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