NAME¶

std::max_element - std::max_element

Synopsis¶

Defined in header <algorithm>
template< class ForwardIt >
ForwardIt max_element( ForwardIt first, ForwardIt last (1) (constexpr since C++17)
);
template< class ExecutionPolicy, class ForwardIt >

ForwardIt max_element( ExecutionPolicy&& policy, (2) (since C++17)

ForwardIt first, ForwardIt last
);
template< class ForwardIt, class Compare >

ForwardIt max_element( ForwardIt first, ForwardIt last, (3) (constexpr since C++17)

Compare comp );
template< class ExecutionPolicy, class ForwardIt, class
Compare >

ForwardIt max_element( ExecutionPolicy&& policy, (4) (since C++17)
ForwardIt first, ForwardIt last,

Compare comp );

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

1) Elements are compared using
operator<
(until C++20)
std::less{}
(since C++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
C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. (since
C++20)

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¶

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

1,2) Exactly \(\scriptsize \max(N-1,0)\)max(N-1,0) comparisons using
operator<
(until C++20)
std::less{}
(since C++20).
3,4) Exactly \(\scriptsize \max(N-1,0)\)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 C++ standards.

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

See also¶

min_element returns the smallest element in a range
(function template)
minmax_element returns the smallest and the largest elements in a range
(C++11) (function template)
max returns the greater of the given values
(function template)
ranges::max_element returns the largest element in a range
(C++20) (niebloid)