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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)
| (2) |
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)

Finds the greatest element in the range `[first, last)`. The first version uses operator< to compare the values, the second version uses the given comparison function `cmp`.

### [edit] Parameters

first, last | - | forward iterators defining the range to examine
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] 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 element in a range (function template) [edit]
max | returns the greater of the given values (function template) [edit]
std::experimental::parallel::max_element (parallelism TS) | parallelized version of `std::max_element` (function template) [edit]

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