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std::ranges::copy, std::ranges::copy_if, std::ranges::copy_result, std::ranges::copy_if_result

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations (on sorted ranges)
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutation operations
Numeric operations
Fold operations
Operations on uninitialized storage
Return types
 
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>
constexpr copy_result<I, O>

    copy( I first, S last, O result );
(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 result );
(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 result, Pred pred, Proj proj = {} );
(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 result, Pred pred, Proj proj = {} );
(4) (since C++20)
Helper types
template< class I, class O >
using copy_result = ranges::in_out_result<I, O>;
(5) (since C++20)
template< class I, class O >
using copy_if_result = ranges::in_out_result<I, O>;
(6) (since C++20)

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

1) Copies all elements in the range [firstlast) starting from first and proceeding to last - 1. The behavior is undefined if result is within the range [firstlast). 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:

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

Contents

[edit] 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

[edit] Return value

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

[edit] 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).

[edit] 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).

[edit] 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;

[edit] 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:

#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

[edit] See also

copies a range of elements in backwards order
(niebloid)[edit]
creates a copy of a range that is reversed
(niebloid)[edit]
copies a number of elements to a new location
(niebloid)[edit]
assigns a range of elements a certain value
(niebloid)[edit]
copies a range of elements omitting those that satisfy specific criteria
(niebloid)[edit]
copies a range of elements to a new location
(function template) [edit]