std::ranges::partition_copy, std::ranges::partition_copy_result - cppreference.com (original) (raw)

1. Copies the elements from the input range [first, last) to two different output ranges depending on the value returned by the predicate pred. The elements that satisfy the predicate pred after projection by proj are copied to the range beginning at out_true. The rest of the elements are copied to the range beginning at out_false. The behavior is undefined if the input range overlaps either of the output ranges.

2. Same as (1), but uses r as the source range, as if using ranges::begin(r) as first, and ranges::end(r) as last.

The function-like entities described on this page are algorithm function objects (informally known as 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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Possible implementation
• 5 Example
• 6 See also

[edit] Parameters

[edit] Return value

{last, o1, o2}, where o1 and o2 are the ends of the output ranges respectively, after the copying is complete.

[edit] Complexity

Exactly ranges::distance(first, last) applications of the corresponding predicate comp and any projection proj.

[edit] Possible implementation

struct partition_copy_fn { template<std::input_iterator I, std::sentinel_for S, std::weakly_incrementable O1, std::weakly_incrementable O2, class Proj = std::identity, std::indirect_unary_predicate< std::projected<I, Proj>> Pred> requires std::indirectly_copyable<I, O1> && std::indirectly_copyable<I, O2> constexpr ranges::partition_copy_result<I, O1, O2> operator()(I first, S last, O1 out_true, O2 out_false, Pred pred, Proj proj = {}) const { for (; first != last; ++first) if (!(pred, std::invoke(proj, *first))) *out_true = *first, ++out_true; else *out_false = *first, ++out_false; return {std::move(first), std::move(out_true), std::move(out_false)}; }   template<ranges::input_range R, std::weakly_incrementable O1, std::weakly_incrementable O2, class Proj = std::identity, std::indirect_unary_predicate<std::projected<iterator_t, Proj>> Pred> requires std::indirectly_copyable<ranges::iterator_t, O1> && std::indirectly_copyable<ranges::iterator_t, O2> constexpr ranges::partition_copy_result<ranges::borrowed_iterator_t, O1, O2> operator()(R&& r, O1 out_true, O2 out_false, Pred pred, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(out_true), std::move(out_false), std::move(pred), std::move(proj)); } };   inline constexpr partition_copy_fn partition_copy {};

[edit] Example

#include #include #include #include #include   int main() { const auto in = {'N', '3', 'U', 'M', '1', 'B', '4', 'E', '1', '5', 'R', '9'};   std::vector o1(size(in)), o2(size(in));   auto pred = [](char c) { return std::isalpha(c); };   auto ret = std::ranges::partition_copy(in, o1.begin(), o2.begin(), pred);   std::ostream_iterator cout {std::cout, " "}; std::cout << "in = "; std::ranges::copy(in, cout); std::cout << "\no1 = "; std::copy(o1.begin(), ret.out1, cout); std::cout << "\no2 = "; std::copy(o2.begin(), ret.out2, cout); std::cout << '\n'; }

Output:

in = N 3 U M 1 B 4 E 1 5 R 9 o1 = N U M B E R o2 = 3 1 4 1 5 9

[edit] See also