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 >

requires std::indirectly_copyable<I, O> (1) (since 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 C++20)
constexpr copy_result<ranges::borrowed_iterator_t<R>, O>

copy( R&& r, O result );
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 > (3) (since 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>, Proj>> Pred > (4) (since 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 C++20)
using copy_result = ranges::in_out_result<I, O>;
template< class I, class O > (6) (since C++20)
using copy_if_result = ranges::in_out_result<I, O>;

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 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 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 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).

Possible implementation¶

copy
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;
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 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 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¶

ranges::copy_backward copies a range of elements in backwards order
(C++20) (niebloid)
ranges::reverse_copy creates a copy of a range that is reversed
(C++20) (niebloid)
ranges::copy_n copies a number of elements to a new location
(C++20) (niebloid)
ranges::fill assigns a range of elements a certain value
(C++20) (niebloid)
ranges::remove_copy copies a range of elements omitting those that satisfy
ranges::remove_copy_if specific criteria
(C++20) (niebloid)
(C++20)
copy copies a range of elements to a new location
copy_if (function template)
(C++11)