std::lexicographical_compare_3way

 

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Technical Specifications

 

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C library
qsort	bsearch

 

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.

See also

compare_3way (C++20)

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