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    std::max_element

    From cppreference.com
     
    C++
     
    Algorithm library
    Constrained algorithms and algorithms on ranges (C++20)
    Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
    Non-modifying sequence operations    
    Batch operations
    (C++17)
    Search operations
    Modifying sequence operations
    Copy operations
    (C++11)
    (C++11)
    (C++11)
    Swap operations
    Transformation operations
    Generation operations
    Removing operations
    Order-changing operations
    (until C++17)(C++11)
    (C++20)(C++20)
    Sampling operations
    (C++17)

    Sorting and related operations
    Partitioning operations
    (C++11)    
    (C++11)

    Sorting operations
    Binary search operations
    (on partitioned ranges)
    Set operations (on sorted ranges)
    Merge operations (on sorted ranges)
    Heap operations
    Minimum/maximum operations
    (C++11)
    (C++17)
    Lexicographical comparison operations
    (C++20)
    Permutation operations


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

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

    1) Elements are compared using operator<(until C++20)std::less{}(since C++20).
    2) Elements are compared using the comparison function comp.
    3,4) Same as (1,2), but executed according to policy.
    These overloads participate in overload resolution only if the value of the following expression is true:

    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)

    Parameters

    first, last - the pair of iterators defining the target range
    comp - 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);

    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.

    policy - the execution policy to use
    Type requirements
    -
    ForwardIt must meet the requirements of LegacyForwardIterator.

    Return value

    Iterator to the greatest element in the target range.

    • If there are multiple greatest elements, returns the iterator to the first one of them.
    • If the target range is empty, returns last.

    Complexity

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

    1) Exactly max(N-1,0) comparisons using operator<(until C++20)std::less{}(since C++20).
    2) Exactly max(N-1,0) applications of the comparator comp.
    3) 𝓞(N) comparisons using operator<(until C++20)std::less{}(since C++20).
    4) 𝓞(N) applications of the comparator comp.

    Exceptions

    3,4) During the execution process:
    • If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
    • If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

    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 (2) 
    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 the target range is empty returns last in this case
    LWG 2150 C++98 the iterator to the first non-smallest element was returned corrected the return value

    See also

    (C++20)
    		 returns the largest element in a range
    (algorithm function object)[edit]
    		returns the smallest element in a range
    (function template & algorithm function object)[edit]
    (C++20)
    (C++11)
    		 returns the smallest and the largest elements in a range
    (function template & algorithm function object)[edit]
    (C++20)
    		returns the greater of the given values
    (function template & algorithm function object)[edit]
    (C++20)