std::ranges::uninitialized_copy, std::ranges::uninitialized_copy_result
From cppreference.com
| Defined in header <memory>
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| Call signature |
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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 );
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(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 );
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(2) | (since C++20) (constexpr since C++26) |
| Helper types |
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template< class I, class O >
using uninitialized_copy_result = ranges::in_out_result<I, O>;
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(3) | (since C++20) |
Let N be ranges::min(ranges::distance(ifirst, ilast), ranges::distance(ofirst, olast)).
1) Constructs 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 | - | the iterator-sentinel pair defining the source range of elements to copy from |
| in_range | - | the range of elements to copy from
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| ofirst, olast | - | the iterator-sentinel pair defining the destination range of elements |
| out_range | - | the destination range
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Return value
As described above.
Complexity
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)
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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{};
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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 |