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std::max_element(3)	       C++ Standard Libary	     std::max_element(3)

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 de-
     tails.
		      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 equiva-
     lent 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  con-
     verted 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 er-
     rors 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-de-
     fined.
	  * 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 retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	       Behavior as  published		    Cor-
     rect 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	    cor-
     rected 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)

http://cppreference.com 	   2024.06.10		     std::max_element(3)
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