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std::lexicographical_compare_3way

Defined in header <algorithm> 
template< class InputIt1, class InputIt2, class Cmp >
constexpr auto lexicographical_compare_3way( InputIt1 first1, InputIt1 last1,
                                             InputIt2 first2, InputIt2 last2,
                                             Cmp comp)
-> std::common_comparison_category_t<decltype(comp(*first1, *first2)), std::strong_ordering>;
 (1) (since C++20) 
template< class InputIt1, class InputIt2 >
constexpr auto lexicographical_compare_3way( InputIt1 first1, InputIt1 last1,
                                             InputIt2 first2, InputIt2 last2);
 (2) (since C++20)

Lexicographically compares two ranges [first1, last1) and [first2, last2) using three-way comparison and produces a result of the strongest applicable comparison category type.

1) Behaves as if defined as follows: 
for ( ; first1 != last1 && first2 != last2; void(++first1), void(++first2) )
  if (auto cmp = comp(*first1,*first2); cmp != 0)
    return cmp;
  return first1 != last1 ? std::strong_ordering::greater :
         first2 != last2 ? std::strong_ordering::less :
                    std::strong_ordering::equal;
2) Behaves as if defined as follows: 
return std::lexicographical_compare_3way(first1, last1, first2, last2,
           [](const auto& t, const auto& u) {
               return std::compare_3way(t, u);
           });

Parameters

first1, last1 - the first range of elements to examine
first2, last2 - the second range of elements to examine
comp - a function object type. The behavior is undefined if its return type is not one of the five comparison category types (strong_equality, weak_equality, strong_ordering, weak_ordering, or partial_ordering)
Type requirements
-InputIt1, InputIt2 must meet the requirements of LegacyInputIterator.

Return value

A comparison category type as defined above.

Example

See also

(C++20)
 compares two values using three-way comparison
(function template)

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