NAME¶

std::ranges::partition_copy,std::ranges::partition_copy_result - std::ranges::partition_copy,std::ranges::partition_copy_result

Synopsis¶

Defined in header <algorithm>
Call signature
template< std::input_iterator I, std::sentinel_for<I> S,

std::weakly_incrementable O1, std::weakly_incrementable O2,
class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred > (since
requires std::indirectly_copyable<I, O1> && (1) C++20)
std::indirectly_copyable<I, O2>
constexpr partition_copy_result<I, O1, O2>
partition_copy( I first, S last, O1 out_true, O2 out_false,

Pred pred, Proj proj = {} );
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<R>,
Proj>> Pred > (2) (since
requires std::indirectly_copyable<ranges::iterator_t<R>, O1> && C++20)
std::indirectly_copyable<ranges::iterator_t<R>, O2>
constexpr partition_copy_result<ranges::borrowed_iterator_t<R>, O1, O2>
partition_copy( R&& r, O1 out_true, O2 out_false,

Pred pred, Proj proj = {} );

Helper types¶

template< class I, class O1, class O2 > (3) (since
using partition_copy_result = ranges::in_out_out_result<I, O1, O2>; C++20)

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 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.

Parameters¶

first, last - the input range of elements to copy from
r - the input range of elements to copy from
out_true - the beginning of the output range for the elements that satisfy pred
out_false - the beginning of the output range for the elements that do not satisfy
pred
pred - predicate to apply to the projected elements
proj - projection to apply to the elements

Return value¶

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

Complexity¶

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

Possible implementation¶

struct partition_copy_fn
{
template<std::input_iterator I, std::sentinel_for<I> 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 (!!std::invoke(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<R>, Proj>> Pred>
requires std::indirectly_copyable<ranges::iterator_t<R>, O1> &&
std::indirectly_copyable<ranges::iterator_t<R>, O2>
constexpr ranges::partition_copy_result<ranges::borrowed_iterator_t<R>, 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 {};

Example¶

// Run this code

#include <algorithm>
#include <cctype>
#include <iostream>
#include <iterator>
#include <vector>

int main()
{
const auto in = {'N', '3', 'U', 'M', '1', 'B', '4', 'E', '1', '5', 'R', '9'};

std::vector<int> 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<char> 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

See also¶

ranges::partition divides a range of elements into two groups
(C++20) (niebloid)
ranges::stable_partition divides elements into two groups while preserving their
(C++20) relative order
(niebloid)
ranges::copy
ranges::copy_if copies a range of elements to a new location
(C++20) (niebloid)
(C++20)
ranges::remove_copy copies a range of elements omitting those that satisfy
ranges::remove_copy_if specific criteria
(C++20) (niebloid)
(C++20)
partition_copy copies a range dividing the elements into two groups
(C++11) (function template)