NAME

std::ranges::copy,std::ranges::copy_if,std::ranges::copy_result, - std::ranges::copy,std::ranges::copy_if,std::ranges::copy_result,

Synopsis

Defined in header <algorithm>
Call signature
template< std::input_iterator I, std::sentinel_for<I> S,
std::weakly_incrementable O >
(since
requires std::indirectly_copyable<I, O> (1) C++20)
constexpr copy_result<I, O>

copy( I first, S last, O result );
template< ranges::input_range R, std::weakly_incrementable O >

requires std::indirectly_copyable<ranges::iterator_t<R>, O> (2) (since
constexpr copy_result<ranges::borrowed_iterator_t<R>, O> C++20)

copy( R&& r, O result );
template< std::input_iterator I, std::sentinel_for<I> S,
std::weakly_incrementable O,

class Proj = std::identity, (since
std::indirect_unary_predicate<std::projected<I, Proj>> Pred > (3) C++20)
requires std::indirectly_copyable<I, O>
constexpr copy_if_result<I, O>

copy_if( I first, S last, O result, Pred pred, Proj proj = {} );
template< ranges::input_range R, std::weakly_incrementable O,

class Proj = std::identity,
std::indirect_unary_predicate<std::projected<ranges::iterator_t<R>, (since
Proj>> Pred > (4) C++20)
requires std::indirectly_copyable<ranges::iterator_t<R>, O>
constexpr copy_if_result<ranges::borrowed_iterator_t<R>, O>

copy_if( R&& r, O result, Pred pred, Proj proj = {} );

Helper types

template< class I, class O > (5) (since
using copy_result = ranges::in_out_result<I, O>; C++20)
template< class I, class O > (6) (since
using copy_if_result = ranges::in_out_result<I, O>; C++20)

Copies the elements in the range, defined by [first, last), to another range
beginning at result.

1) Copies all elements in the range [first, last) starting from first and proceeding
to last - 1. The behavior is undefined if result is within the range [first, last).
In this case, ranges::copy_backward may be used instead.
3) Only copies the elements for which the predicate pred returns true. The relative
order of the elements that are copied is preserved. The behavior is undefined if the
source and the destination ranges overlap.
2,4) Same as (1,3), 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 may not be specified when calling any of them.
* None of them is visible to argument-dependent lookup.
* When one of them is found by normal unqualified lookup for the name to the left
of the function-call operator, it inhibits argument-dependent lookup.

In practice, they may be implemented as function objects, or with special compiler
extensions.

Parameters

first, last - the range of elements to copy
r - the range of elements to copy
result - the beginning of the destination range.
pred - predicate to apply to the projected elements
proj - projection to apply to the elements

Return value

A ranges::in_out_result containing an input iterator equal to last and an output
iterator past the last element copied.

Complexity

1-2) Exactly (last - first) assignments
3-4) Exactly (last - first) applications of the predicate and projection, between
0 and (last - first) assignments (assignment for every element for which
predicate returns true, dependent on predicate and input data)

Notes

In practice, implementations of std::ranges::copy avoid multiple assignments and use
bulk copy functions such as std::memmove if the value type is TriviallyCopyable and
the iterator types satisfy contiguous_iterator.

When copying overlapping ranges, std::ranges::copy is appropriate when copying to
the left (beginning of the destination range is outside the source range) while
std::ranges::copy_backward is appropriate when copying to the right (end of the
destination range is outside the source range).

Possible implementation

First version

struct copy_fn {
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O >
requires std::indirectly_copyable<I, O>
constexpr ranges::copy_result<I, O> operator()( I first, S last, O result ) const
{
for (; first != last; ++first, (void)++result) {
*result = *first;
}
return {std::move(first), std::move(result)};
}

template< ranges::input_range R, std::weakly_incrementable O >
requires std::indirectly_copyable<ranges::iterator_t<R>, O>
constexpr ranges::copy_result<ranges::borrowed_iterator_t<R>, O>
operator()( R&& r, O result ) const
{
return (*this)(ranges::begin(r), ranges::end(r), std::move(result));
}
};

inline constexpr copy_fn copy;

Second version

struct copy_if_fn {
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O,
class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred >
requires std::indirectly_copyable<I, O>
constexpr ranges::copy_if_result<I, O>
operator()( I first, S last, O result, Pred pred, Proj proj = {} ) const
{
for (; first != last; ++first) {
if (std::invoke(pred, std::invoke(proj, *first))) {
*result = *first;
++result;
}
}

return {std::move(first), std::move(result)};
}

template< ranges::input_range R, std::weakly_incrementable O,
class Proj = std::identity,
std::indirect_unary_predicate<
std::projected<ranges::iterator_t<R>, Proj>> Pred >
requires std::indirectly_copyable<ranges::iterator_t<R>, O>
constexpr ranges::copy_if_result<ranges::borrowed_iterator_t<R>, O>
operator()( R&& r, O result, Pred pred, Proj proj = {} ) const
{
return (*this)(ranges::begin(r), ranges::end(r),
std::move(result),
std::ref(pred), std::ref(proj));
}
};

inline constexpr copy_if_fn copy_if;

Example

The following code uses copy to both copy the contents of one vector to another and
to display the resulting vector:

// Run this code

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

int main()
{
std::vector<int> from_vector(10);
std::iota(from_vector.begin(), from_vector.end(), 0);

std::vector<int> to_vector;

namespace ranges = std::ranges;
ranges::copy(from_vector.begin(), from_vector.end(),
std::back_inserter(to_vector));
// or, alternatively,
// std::vector<int> to_vector(from_vector.size());
// ranges::copy(from_vector.begin(), from_vector.end(), to_vector.begin());
// either way is equivalent to
// std::vector<int> to_vector = from_vector;

std::cout << "to_vector contains: ";

ranges::copy(to_vector, std::ostream_iterator<int>(std::cout, " "));
std::cout << '\n';

std::cout << "odd numbers in to_vector are: ";

ranges::copy_if(to_vector, std::ostream_iterator<int>(std::cout, " "),
[](int x) { return (x % 2) == 1; });
std::cout << '\n';
}

Output:

to_vector contains: 0 1 2 3 4 5 6 7 8 9
odd numbers in to_vector are: 1 3 5 7 9