26 Algorithms library [algorithms]

26.8 Sorting and related operations [alg.sorting]

26.8.7 Set operations on sorted structures [alg.set.operations]

26.8.7.5 set_difference [set.difference]

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template<class InputIterator1, class InputIterator2, class OutputIterator> constexpr OutputIterator set_difference(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class ForwardIterator> ForwardIterator set_difference(ExecutionPolicy&& exec, ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, ForwardIterator result); template<class InputIterator1, class InputIterator2, class OutputIterator, class Compare> constexpr OutputIterator set_difference(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class ForwardIterator, class Compare> ForwardIterator set_difference(ExecutionPolicy&& exec, ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2, ForwardIterator2 last2, ForwardIterator result, Compare comp); template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2, weakly_incrementable O, class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity> requires mergeable<I1, I2, O, Comp, Proj1, Proj2> constexpr ranges::set_difference_result<I1, O> ranges::set_difference(I1 first1, S1 last1, I2 first2, S2 last2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); template<input_range R1, input_range R2, weakly_incrementable O, class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity> requires mergeable<iterator_t<R1>, iterator_t<R2>, O, Comp, Proj1, Proj2> constexpr ranges::set_difference_result<borrowed_iterator_t<R1>, O> ranges::set_difference(R1&& r1, R2&& r2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); template<execution-policy Ep, random_access_iterator I1, sized_sentinel_for<I1> S1, random_access_iterator I2, sized_sentinel_for<I2> S2, random_access_iterator O, sized_sentinel_for<O> OutS, class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity> requires mergeable<I1, I2, O, Comp, Proj1, Proj2> ranges::set_difference_result<I1, O> ranges::set_difference(Ep&& exec, I1 first1, S1 last1, I2 first2, S2 last2, O result, OutS result_last, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}); template<execution-policy Ep, sized-random-access-range R1, sized-random-access-range R2, sized-random-access-range OutR, class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity> requires mergeable<iterator_t<R1>, iterator_t<R2>, iterator_t<OutR>, Comp, Proj1, Proj2> ranges::set_difference_result<borrowed_iterator_t<R1>, borrowed_iterator_t<OutR>> ranges::set_difference(Ep&& exec, R1&& r1, R2&& r2, OutR&& result_r, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
1
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Let:
  • (1.1)
    comp be less{}, and proj1 and proj2 be identity{} for the overloads with no parameters by those names;
  • (1.2)
    M be the number of elements in [first1, last1) that are not present in [first2, last2);
  • (1.3)
    result_last be result + M for the overloads with no parameter result_last or result_r;
  • (1.4)
    N be min(M,  result_last - result).
2
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Preconditions: The ranges [first1, last1) and [first2, last2) are sorted with respect to comp and proj1 or proj2, respectively.
The resulting range does not overlap with either of the original ranges.
3
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Effects: Copies N elements of the range [first1, last1) which are not present in the range [first2, last2) to the range [result, result + N).
The elements in the constructed range are sorted.
4
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Returns:
  • (4.1)
    result_last for the overloads in namespace std.
  • (4.2)
    {last1, result + N} for the overloads in namespace ranges, if N is equal to M.
  • (4.3)
    Otherwise, {j1, result_last} for the overloads in namespace ranges, where the iterator j1 points to positions past the last copied or skipped elements in [first1, last1) and [first2, last2), respectively.
5
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Complexity: At most 2 * ((last1 - first1) + (last2 - first2)) - 1 comparisons and applications of each projection.
6
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Remarks: If [first1, last1) contains m elements that are equivalent to each other and [first2, last2) contains n elements that are equivalent to them, the last elements from [first1, last1) are copied to the output range, in order.