25 Algorithms library [algorithms]

25.7 Sorting and related operations [alg.sorting]

25.7.11 Three-way comparison algorithms [alg.three.way]

template<class InputIterator1, class InputIterator2, class Cmp> constexpr auto lexicographical_compare_three_way(InputIterator1 b1, InputIterator1 e1, InputIterator2 b2, InputIterator2 e2, Cmp comp) -> common_comparison_category_t<decltype(comp(*b1, *b2)), strong_ordering>;
Mandates: decltype(comp(*b1, *b2)) is a comparison category type.
Effects: Lexicographically compares two ranges and produces a result of the strongest applicable comparison category type.
Equivalent to:
for ( ; b1 != e1 && b2 != e2; void(++b1), void(++b2) )
  if (auto cmp = comp(*b1,*b2); cmp != 0)
    return cmp;
return b1 != e1 ? strong_ordering::greater :
       b2 != e2 ? strong_ordering::less :
                  strong_ordering::equal;
template<class InputIterator1, class InputIterator2> constexpr auto lexicographical_compare_three_way(InputIterator1 b1, InputIterator1 e1, InputIterator2 b2, InputIterator2 e2);
Effects: Equivalent to:
return lexicographical_compare_three_way(b1, e1, b2, e2, compare_three_way());