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      std::max_element

      From cppreference.com
      <cpp‎ |algorithm
       
       
      Algorithm library
      Constrained algorithms and algorithms on ranges(C++20)
      Constrained algorithms, e.g.ranges::copy,ranges::sort, ...
      Execution policies(C++17)
      Sorting and related operations
      Partitioning operations
      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)
      max_element

      Lexicographical comparison operations
      Permutation operations
      C library
      Numeric operations
      Operations on uninitialized memory
       
      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,

                             ForwardIt first, ForwardIt last);
      		 (2)(since C++17)
      template<class ForwardIt,class Compare>

      ForwardIt max_element( ForwardIt first, ForwardIt last,

                             Compare comp);
      		 (3)(constexpr 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 range[first, last).

      1) Elements are compared usingoperator<(until C++20)std::less{}(since C++20).
      3) Elements are compared using the comparison functioncomp.
      2,4) Same as(1,3), but executed according topolicy.
      These overloads participate in overload resolution only if all following conditions are satisfied:

      std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> istrue.

      		(until C++20)

      std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> istrue.

      		(since C++20)

      Contents

      [edit]Parameters

      first, last - the pair of iterators defining therange of elements to examine
      policy - theexecution policy to use
      comp - comparison function object (i.e. an object that satisfies the requirements ofCompare) which returnstrue if the first argument isless 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 haveconst&, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const)Type1 andType2 regardless ofvalue category (thus,Type1& is not allowed, nor isType1 unless forType1 a move is equivalent to a copy(since C++11)).
      The typesType1 andType2 must be such that an object of typeForwardIt can be dereferenced and then implicitly converted to both of them.

      Type requirements
      -
      ForwardIt must meet the requirements ofLegacyForwardIterator.

      [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. Returnslast if the range is empty.

      [edit]Complexity

      Given\(\scriptsize N\)N asstd::distance(first, last):

      1,2) Exactly\(\scriptsize \max(N-1,0)\)max(N-1,0) comparisons usingoperator<(until C++20)std::less{}(since C++20).
      3,4) Exactly\(\scriptsize \max(N-1,0)\)max(N-1,0) applications of the comparison functioncomp.

      [edit]Exceptions

      The overloads with a template parameter namedExecutionPolicy report errors as follows:

      • If execution of a function invoked as part of the algorithm throws an exception andExecutionPolicy is one of thestandard policies,std::terminate is called. For any otherExecutionPolicy, the behavior is implementation-defined.
      • If the algorithm fails to allocate memory,std::bad_alloc is thrown.

      [edit]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;}

      [edit]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 9Absolute max element found at index 2 has value -14

      [edit]Defect reports

      The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

      DRApplied toBehavior as publishedCorrect behavior
      LWG 212C++98the return value was not specified if[first, last) is emptyreturnslast in this case
      LWG 2150C++98the iterator to the first non-smallest element was returnedcorrected the return value

      [edit]See also

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