std::ranges::uninitialized_copy, std::ranges::uninitialized_copy_result

 

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voidify (exposition only*) Uninitialized memory algorithms uninitialized_copy uninitialized_fill uninitialized_move (C++17) uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy (C++17) destroy_at (C++17) uninitialized_copy_n (C++11) uninitialized_fill_n uninitialized_move_n (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) destroy_n (C++17) construct_at (C++20) Constrained uninitialized memory algorithms ranges::uninitialized_copy (C++20) ranges::uninitialized_fill (C++20) ranges::uninitialized_move (C++20) ranges::construct_at (C++20) ranges::destroy (C++20) ranges::destroy_n (C++20) ranges::destroy_at (C++20) ranges::uninitialized_copy_n (C++20) ranges::uninitialized_fill_n (C++20) ranges::uninitialized_move_n (C++20) ranges::uninitialized_default_construct (C++20) ranges::uninitialized_value_construct (C++20) ranges::uninitialized_default_construct_n (C++20)  ranges::uninitialized_value_construct_n (C++20) C Library malloc calloc realloc aligned_alloc (C++17) free

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Defined in header <memory>
Call signature
template< std::input_iterator I, std::sentinel_for<I> S1,           no-throw-forward-iterator O, no-throw-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, no-throw-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)
Helper types
template< class I, class O > using uninitialized_copy_result = ranges::in_out_result<I, O>;	(3)	(since C++20)

Let \(\scriptsize N\)N be ranges::min(ranges::distance(ifirst, ilast), ranges::distance(ofirst, olast)).

1) Constructs \(\scriptsize N\)N elements elements from the range [ifirst, ilast) to an uninitialized memory area [ofirst, olast) 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) Equivalent to return ranges::uninitialized_copy(ranges::begin(in_range), ranges::end(in_range),
                                  ranges::begin(out_range), ranges::end(out_range));.

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	-	iterator-sentinel pair denoting the range of elements to copy from
in_range	-	the range of elements to copy from
ofirst, olast	-	iterator-sentinel pair denoting the destination range
out_range	-	the destination range

Return value

As described above.

Complexity

\(\scriptsize\mathcal{O}(N)\)𝓞(N).

Exceptions

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

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_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, no-throw-forward-iterator O, no-throw-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, no-throw-forward-range OR> requires std::constructible_from<ranges::range_value_t<OR>, constexpr ranges::range_reference_t<IR>> 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::end(out_range)); } };   inline constexpr uninitialized_copy_fn uninitialized_copy{};

Example

Run this code

#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"};

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3870	C++20	this algorithm might create objects on a const storage	kept disallowed

See also

ranges::uninitialized_copy_n (C++20)	copies a number of objects to an uninitialized area of memory (algorithm function object)
uninitialized_copy	copies a range of objects to an uninitialized area of memory (function template)