std::ranges::copy, std::ranges::copy_if, std::ranges::copy_result, std::ranges::copy_if_result
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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template< std::input_iterator I, std::sentinel_for<I> S,
std::weakly_incrementable O >
requires std::indirectly_copyable<I, O>
constexpr copy_result<I, O>
copy( I first, S last, O d_first );
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(1) | (since C++20) |
template< ranges::input_range R, std::weakly_incrementable O >
requires std::indirectly_copyable<ranges::iterator_t<R>, O>
constexpr copy_result<ranges::borrowed_iterator_t<R>, O>
copy( R&& r, O d_first );
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(2) | (since C++20) |
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 copy_if_result<I, O>
copy_if( I first, S last, O d_first, Pred pred, Proj proj = {} );
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(3) | (since C++20) |
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 copy_if_result<ranges::borrowed_iterator_t<R>, O>
copy_if( R&& r, O d_first, Pred pred, Proj proj = {} );
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(4) | (since C++20) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
std::random_access_iterator O, std::sized_sentinel_for<O> OutS >
requires std::indirectly_copyable<I, O>
copy_result<I, O>
copy( Ep&& policy, I first, S last, O d_first, OutS d_last );
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(5) | (since C++26) |
template< /*execution-policy*/ Ep,
/*sized-random-access-range*/ R,
/*sized-random-access-range*/ OutR >
requires std::indirectly_copyable<ranges::iterator_t<R>,
ranges::iterator_t<OutR>>
copy_result<ranges::borrowed_iterator_t<R>,
ranges::borrowed_iterator_t<OutR>>
copy( Ep&& policy, R&& r, OutR&& d_r );
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(6) | (since C++26) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S,
std::random_access_iterator O, std::sized_sentinel_for<O> OutS,
class Proj = std::identity,
std::indirect_unary_predicate<std::projected<I, Proj>> Pred >
requires std::indirectly_copyable<I, O>
copy_if_result<I, O>
copy_if( Ep&& policy, I first, S last, O d_first, OutS d_last,
Pred pred, Proj proj = {} );
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(7) | (since C++26) |
template< /*execution-policy*/ Ep,
/*sized-random-access-range*/ R,
/*sized-random-access-range*/ OutR,
class Proj = std::identity,
std::indirect_unary_predicate
<std::projected<ranges::iterator_t<R>, Proj>> Pred >
requires std::indirectly_copyable<ranges::iterator_t<R>,
ranges::iterator_t<OutR>>
copy_if_result<ranges::borrowed_iterator_t<R>,
ranges::borrowed_iterator_t<OutR>>
copy_if( Ep&& policy, R&& r, OutR&& d_r,
Pred pred, Proj proj = {} );
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(8) | (since C++26) |
| Helper types |
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template< class I, class O >
using copy_result = ranges::in_out_result<I, O>;
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(9) | (since C++20) |
template< class I, class O >
using copy_if_result = ranges::in_out_result<I, O>;
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(10) | (since C++20) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
Copies the elements in the source range [first, last) or r to the destination range.
1,2)
copy copies all elements in the source range, starting from the beginning and proceeding to the end. The destination range begins at d_first. If
d_first is in the source range, the behavior is undefined.3,4)
copy_if only copies the elements (projected by proj) for which the predicate pred returns true. The destination range begins at d_first. If the source and destination ranges overlap, the behavior is undefined.
5-8) Same as (1-4), but the copy order is determined by
policy. If the destination range is exhausted before reaching the end of the source range, the remaining elements in the source range will not be copied. If the source and destination ranges overlap, the behavior is undefined.
5,7) The destination range is
[d_first, d_last).6,8) The destination range is
d_r.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.
Parameters
| first, last | - | the iterator-sentinel pair defining the source range |
| r | - | the source range |
| d_first | - | the beginning of the destination range |
| d_last | - | the sentinel of the destination range |
| d_r | - | the destination range |
| pred | - | the predicate to be applied to the (projected) elements |
| proj | - | the projection to be applied to the elements in the source range |
| policy | - | the execution policy to use |
Return value
A ranges::copy_result or ranges::copy_if_result object where:
- The data member
inholds the an iterator past the last copied element in the source range, or an iterator to the beginning of the source range if no element is copied. - The data member
outholds and an iterator past the last copy-assigned element in the destination range, or an iterator to the beginning of the destination range if no element is copied.
Complexity
Given
- N1 as
ranges::distance(first, last)orranges::distance(r), and - N2 as
ranges::distance(d_first, d_last)orranges::distance(d_r):
1,2) Exactly N1 assignments.
3,4) Exactly N1
pred and proj, and at most N1 assignments.5,6) Exactly min(N1,N2) assignments.
7,8) Exactly min(N1,N2)
pred and proj, and at most min(N1,N2) assignments.Exceptions
5-8) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
Notes
In practice, implementations of 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, ranges::copy is appropriate when copying to the left (beginning of the destination range is outside the source range) while ranges::copy_backward is appropriate when copying to the right (end of the destination range is outside the source range).
ranges::copy_if is stable. The relative order of the elements that are copied is preserved.
For parallel algorithm overloads, there may be a performance cost if std::iter_value_t<I> or ranges::range_value_t<R> does not model move_constructible.
Possible implementation
| copy |
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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 d_first) const
{
for (; first != last; ++first, (void)++d_first)
*d_first = *first;
return {std::move(first), std::move(d_first)};
}
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 d_first) const
{
return (*this)(ranges::begin(r), ranges::end(r), std::move(d_first));
}
template<ranges::forward_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 d_first) const
{
return (*this)(ranges::begin(r),
ranges::next(ranges::begin(r), ranges::end(r)),
std::move(d_first));
}
};
inline constexpr copy_fn copy;
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| copy_if |
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 d_first, Pred pred, Proj proj = {}) const
{
for (; first != last; ++first)
if (std::invoke(pred, std::invoke(proj, *first)))
{
*d_first = *first;
++d_first;
}
return {std::move(first), std::move(d_first)};
}
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 d_first, Pred pred, Proj proj = {}) const
{
return (*this)(ranges::begin(r), ranges::end(r),
std::move(d_first), std::ref(pred), std::ref(proj));
}
template<ranges::forward_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 d_first, Pred pred, Proj proj = {}) const
{
return (*this)(ranges::begin(r),
ranges::next(ranges::begin(r), ranges::end(r)),
std::move(d_first), std::ref(pred), std::ref(proj));
}
};
inline constexpr copy_if_fn copy_if;
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Example
The following code uses ranges::copy to both copy the contents of one std::vector to another and to display the resulting std::vector.
Run this code
#include <algorithm>
#include <iostream>
#include <iterator>
#include <numeric>
#include <vector>
int main()
{
std::vector<int> source(10);
std::iota(source.begin(), source.end(), 0);
std::vector<int> destination;
std::ranges::copy(source.begin(), source.end(), std::back_inserter(destination));
// or, alternatively,
// std::vector<int> destination(source.size());
// std::ranges::copy(source.begin(), source.end(), destination.begin());
// either way is equivalent to
// std::vector<int> destination = source;
std::cout << "Destination contains: ";
std::ranges::copy(destination, std::ostream_iterator<int>(std::cout, " "));
std::cout << '\n';
std::cout << "Odd numbers in destination are: ";
std::ranges::copy_if(destination, std::ostream_iterator<int>(std::cout, " "),
[](int x) { return (x % 2) == 1; });
std::cout << '\n';
}
Output:
Destination contains: 0 1 2 3 4 5 6 7 8 9
Odd numbers in destination are: 1 3 5 7 9
See also
(C++11) |
copies a range of elements to a new location (function template) |
(C++20) |
copies a range of elements in backwards order (algorithm function object) |
(C++20) |
creates a copy of a range that is reversed (algorithm function object) |
(C++20) |
copies a number of elements to a new location (algorithm function object) |
(C++20) |
assigns a range of elements a certain value (algorithm function object) |
(C++20)(C++20) |
copies a range of elements omitting those that satisfy specific criteria (algorithm function object) |