std::ranges::set_difference, std::ranges::set_difference_result
| Defined in header <algorithm>
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| Call signature |
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| template< std::input_iterator I1, std::sentinel_for<I1> S1, std::input_iterator I2, std::sentinel_for<I2> S2, |
(1) | (since C++20) |
| template< ranges::input_range R1, ranges::input_range R2, std::weakly_incrementable O, class Comp = ranges::less, |
(2) | (since C++20) |
| Helper types |
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| template< class I, class O > using set_difference_result = ranges::in_out_result<I, O>; |
(3) | (since C++20) |
Copies the elements from the sorted input range [first1, last1) which are not found in the sorted input range [first2, last2) to the output range beginning at result.
The behavior is undefined if
- the input ranges are not sorted with respect to comp and proj1 or proj2, respectively, or
- the resulting range overlaps with either of the input ranges.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
Parameters
| first1, last1 | - | iterator-sentinel pair denoting the first sorted input range |
| first2, last2 | - | iterator-sentinel pair denoting the second sorted input range |
| r1 | - | the first sorted input range |
| r2 | - | the second sorted input range |
| result | - | the beginning of the output range |
| comp | - | comparator to apply to the projected elements |
| proj1 | - | projection to apply to the elements in the first range |
| proj2 | - | projection to apply to the elements in the second range |
Return value
{last1, result_last}, where result_last is the end of the constructed range.
Complexity
At most 2·(N1+N2)-1 comparisons and applications of each projection, where N1 and N2 are ranges::distance(first1, last1) and ranges::distance(first2, last2), respectively.
Possible implementation
struct set_difference_fn { template<std::input_iterator I1, std::sentinel_for<I1> S1, std::input_iterator I2, std::sentinel_for<I2> S2, std::weakly_incrementable O, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity> requires std::mergeable<I1, I2, O, Comp, Proj1, Proj2> constexpr ranges::set_difference_result<I1, O> operator()(I1 first1, S1 last1, I2 first2, S2 last2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const { while (!(first1 == last1 or first2 == last2)) { if (std::invoke(comp, std::invoke(proj1, *first1), std::invoke(proj2, *first2))) { *result = *first1; ++first1; ++result; } else if (std::invoke(comp, std::invoke(proj2, *first2), std::invoke(proj1, *first1))) ++first2; else { ++first1; ++first2; } } return ranges::copy(std::move(first1), std::move(last1), std::move(result)); } template<ranges::input_range R1, ranges::input_range R2, std::weakly_incrementable O, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity> requires std::mergeable<ranges::iterator_t<R1>, ranges::iterator_t<R2>, O, Comp, Proj1, Proj2> constexpr ranges::set_difference_result<ranges::borrowed_iterator_t<R1>, O> operator()(R1&& r1, R2&& r2, O result, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const { return (*this)(ranges::begin(r1), ranges::end(r1), ranges::begin(r2), ranges::end(r2), std::move(result), std::move(comp), std::move(proj1), std::move(proj2)); } }; inline constexpr set_difference_fn set_difference {}; |
Example
#include <algorithm> #include <cassert> #include <iostream> #include <iterator> #include <string_view> #include <vector> auto print = [](const auto& v, std::string_view end = "") { std::cout << "{ "; for (auto n{v.size()}; auto i : v) std::cout << i << (--n ? ", " : " "); std::cout << "} " << end; }; struct Order // a struct with some very interesting data { int order_id{}; friend std::ostream& operator<<(std::ostream& os, const Order& ord) { return os << '{' << ord.order_id << '}'; } }; int main() { const auto v1 = {1, 2, 5, 5, 5, 9}; const auto v2 = {2, 5, 7}; std::vector<int> diff{}; std::ranges::set_difference(v1, v2, std::back_inserter(diff)); print(v1, "∖ "); print(v2, "= "); print(diff, "\n\n"); // We want to know which orders "cut" between old and new states: const std::vector<Order> old_orders{{1}, {2}, {5}, {9}}; const std::vector<Order> new_orders{{2}, {5}, {7}}; std::vector<Order> cut_orders(old_orders.size() + new_orders.size()); auto [old_orders_end, cut_orders_last] = std::ranges::set_difference(old_orders, new_orders, cut_orders.begin(), {}, &Order::order_id, &Order::order_id); assert(old_orders_end == old_orders.end()); std::cout << "old orders = "; print(old_orders, "\n"); std::cout << "new orders = "; print(new_orders, "\n"); std::cout << "cut orders = "; print(cut_orders, "\n"); cut_orders.erase(cut_orders_last, end(cut_orders)); std::cout << "cut orders = "; print(cut_orders, "\n"); }
Output:
{ 1, 2, 5, 5, 5, 9 } ∖ { 2, 5, 7 } = { 1, 5, 5, 9 }
old orders = { {1}, {2}, {5}, {9} }
new orders = { {2}, {5}, {7} }
cut orders = { {1}, {9}, {0}, {0}, {0}, {0}, {0} }
cut orders = { {1}, {9} }See also
| (C++20) |
computes the union of two sets (niebloid) |
| (C++20) |
computes the intersection of two sets (niebloid) |
| computes the symmetric difference between two sets (niebloid) | |
| (C++20) |
returns true if one sequence is a subsequence of another (niebloid) |
| computes the difference between two sets (function template) |
