27 Algorithms library [algorithms]

27.8 Sorting and related operations [alg.sorting]

27.8.12 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)
      -> decltype(comp(*b1, *b2));

Let N be min(e1 - b1, e2 - b2).

Let E(n) be comp(*(b1 + n), *(b2 + n)).

Mandates: decltype(comp(*b1, *b2)) is a comparison category type.

Returns: E(i), where i is the smallest integer in [0, N) such that E(i) != 0 is true, or (e1 - b1) <=> (e2 - b2) if no such integer exists.

Complexity: At most N applications of comp.

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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());