std::ranges::uninitialized_copy, std::ranges::uninitialized_copy_result - cppreference.com

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Defined in header `<memory>`
Call signature
template< std::input_iterator I, std::sentinel_for<I> S1, /nothrow-forward-iterator/ O, /nothrow-sentinel-for/<O> S2 > requires std::constructible_from<std::iter_value_t<O>, std::iter_reference_t<I>> uninitialized_copy_result<I, O> uninitialized_copy( I ifirst, S1 ilast, O ofirst, S2 olast );	(1)	(since C++20) (constexpr since C++26)
template< ranges::input_range IR, /nothrow-forward-range/ OR > requires std::constructible_from<ranges::range_value_t<OR>, ranges::range_reference_t<IR>> uninitialized_copy_result<ranges::borrowed_iterator_t<IR>, ranges::borrowed_iterator_t<OR>> uninitialized_copy( IR&& in_range, OR&& out_range );	(2)	(since C++20) (constexpr since C++26)
template< /execution-policy/ Ep, std::random_access_iterator I, std::sized_sentinel_for<I> S1, /nothrow-random-access-iterator/ O, /nothrow-sized-sentinel-for/<O> S2 > requires std::constructible_from<std::iter_value_t<O>, std::iter_reference_t<I>> uninitialized_copy_result<I, O> uninitialized_copy( Ep&& policy, I ifirst, S1 ilast, O ofirst, S2 olast );	(3)	(since C++26)
template< /execution-policy/ Ep, /sized-random-access-range/ IR, /nothrow-sized-random-access-range/ OR > requires std::constructible_from<ranges::range_value_t<OR>, ranges::range_reference_t<IR>> uninitialized_copy_result<ranges::borrowed_iterator_t<IR>, ranges::borrowed_iterator_t<OR>> uninitialized_copy( Ep&& policy, IR&& in_range, OR&& out_range );	(4)	(since C++26)
Helper types
template< class I, class O > using uninitialized_copy_result = ranges::in_out_result<I, O>;	(5)	(since C++20)

For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page; for the definition of other exposition-only concepts, see this page.

1) Constructs elements in the destination range [ofirst, olast) from elements in the source range [ifirst, ilast) as if by

for (; ifirst != ilast && ofirst != olast; ++ofirst, (void)++ifirst)
::new (voidify(*ofirst)) std::remove_reference_t<std::iter_reference_t<O>>(*ifirst);
return {std::move(ifirst), ofirst};

If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.

If [ofirst, olast) overlaps with [ifirst, ilast), the behavior is undefined.

2) Same as (1), but uses in_range as the source range and out_range as the destination range.

3,4) Same as (1,2), but executed according to policy.

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

ifirst, ilast	-	the iterator-sentinel pair defining the source range of elements to copy from
in_range	-	the `range` of elements to copy from
ofirst, olast	-	the iterator-sentinel pair defining the destination range of elements
out_range	-	the destination `range`
policy	-	the execution policy to use

Return value

As described above.

Exceptions

Any exception thrown on construction of the elements in the destination range.

3,4) 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

An implementation may improve the efficiency of ranges::uninitialized_copy if the value type of the output range is TrivialType.

Feature-test macro	Value	Std	Feature
`__cpp_lib_parallel_algorithm`	`202506L`	(C++26)	Parallel range algorithms
`__cpp_lib_raw_memory_algorithms`	`202411L`	(C++26)	`constexpr` for specialized `<memory>` algorithms, (1,2)

Possible implementation

struct uninitialized_copy_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S1,
             /*nothrow-forward-iterator*/ O, /*nothrow-sentinel-for*/<O> S2>
        requires std::constructible_from<std::iter_value_t<O>, std::iter_reference_t<I>>
    constexpr ranges::uninitialized_copy_result<I, O>
        operator()(I ifirst, S1 ilast, O ofirst, S2 olast) const
    {
        O current{ofirst};
        try
        {
            for (; !(ifirst == ilast or current == olast); ++ifirst, ++current)
                ranges::construct_at(std::addressof(*current), *ifirst);
            return {std::move(ifirst), std::move(current)};
        }
        catch (...) // rollback: destroy constructed elements
        {
            for (; ofirst != current; ++ofirst)
                ranges::destroy_at(std::addressof(*ofirst));
            throw;
        }
    }
    
    template<ranges::input_range IR, /*nothrow-forward-range*/ OR>
        requires std::constructible_from<ranges::range_value_t<OR>,
                                         ranges::range_reference_t<IR>>
    constexpr ranges::uninitialized_copy_result<ranges::borrowed_iterator_t<IR>,
                                                ranges::borrowed_iterator_t<OR>>
        operator()(IR&& in_range, OR&& out_range) const
    {
        return (*this)(ranges::begin(in_range), ranges::end(in_range),
                       ranges::begin(out_range),
                       ranges::next(ranges::begin(out_range), ranges::end(out_range)));
    }
    
    template<ranges::forward_range IR, /*nothrow-forward-range*/ OR>
        requires std::constructible_from<ranges::range_value_t<OR>,
                                         ranges::range_reference_t<IR>>
    constexpr ranges::uninitialized_copy_result<ranges::borrowed_iterator_t<IR>,
                                                ranges::borrowed_iterator_t<OR>>
        operator()(IR&& in_range, OR&& out_range) const
    {
        return (*this)(ranges::begin(in_range),
                       ranges::next(ranges::begin(in_range), ranges::end(in_range)),
                       ranges::begin(out_range),
                       ranges::next(ranges::begin(out_range), ranges::end(out_range)));
    }
};

inline constexpr uninitialized_copy_fn uninitialized_copy{};

Example

#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <memory>
#include <string>

int main()
{
    const char* v[]{"This", "is", "an", "example"};
    
    if (const auto sz{std::size(v)};
        void* pbuf = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz))
    {
        try
        {
            auto first{static_cast<std::string*>(pbuf)};
            auto last{first + sz};
            std::ranges::uninitialized_copy(std::begin(v), std::end(v), first, last);
            
            std::cout << "{";
            for (auto it{first}; it != last; ++it)
                std::cout << (it == first ? "" : ", ") << std::quoted(*it);
            std::cout << "};\n";
            
            std::ranges::destroy(first, last);
        }
        catch (...)
        {
            std::cout << "uninitialized_copy exception\n";
        }
        std::free(pbuf);
    }
}

Output:

{"This", "is", "an", "example"};