NAME

std::max_element - std::max_element

Synopsis

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

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

Parameters

first, last - forward iterators defining the range to examine
policy - the execution policy to use. See execution policy for details.
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);
comp -
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) << '\n';
}

Output:

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