std::ranges::uninitialized_move_n, std::ranges::uninitialized_move_n_result
From cppreference.com
| Defined in header <memory>
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| Call signature |
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template< std::input_iterator I,
/*nothrow-forward-iterator*/ O, /*nothrow-sentinel-for*/<O> S >
requires std::constructible_from<std::iter_value_t<O>,
std::iter_rvalue_reference_t<I>>
uninitialized_move_n_result<I, O>
uninitialized_move_n( I ifirst, std::iter_difference_t<I> count,
O ofirst, S olast );
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(1) | (since C++20) (constexpr since C++26) |
template< /*execution-policy*/ Ep, std::random_access_iterator I,
/*nothrow-random-access-iterator*/ O,
/*nothrow-sized-sentinel-for*/<O> S >
requires std::constructible_from<std::iter_value_t<O>,
std::iter_rvalue_reference_t<I>>
uninitialized_move_n_result<I, O>
uninitialized_move_n( Ep&& policy, I ifirst,
std::iter_difference_t<I> count,
O ofirst, S olast );
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(2) | (since C++26) |
| Helper types |
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template< class I, class O >
using uninitialized_move_n_result = ranges::in_out_result<I, O>;
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(3) | (since C++20) |
For the definition of /*execution-policy*/, 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 + [0, count) as if by
auto ret = ranges::uninitialized_move(std::counted_iterator(std::move(ifirst), count),
std::default_sentinel, ofirst, olast);
return {std::move(ret.in).base(), ret.out};
If an exception is thrown during the initialization then the objects that already constructed in
[ofirst, olast) are destroyed in an unspecified order. Also, the objects in the input range beginning at ifirst, that were already moved, are left in a valid but unspecified state. If
[ofirst, olast) overlaps with ifirst + [0, count), the behavior is undefined.2) Same as (1), 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 | - | the beginning of the input range of elements to move from |
| ofirst, olast | - | the iterator-sentinel pair defining the output range of elements to initialize |
| count | - | the number of elements to move |
| policy | - | the execution policy to use |
Return value
As described above.
Exceptions
Any exception thrown on construction of the elements in the destination range.
2) 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 the ranges::uninitialized_move_n (by using e.g. ranges::copy_n) 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)
|
Possible implementation
struct uninitialized_move_n_fn
{
template<std::input_iterator I,
/*nothrow-forward-iterator*/ O, /*nothrow-sentinel-for*/<O> S>
requires std::constructible_from<std::iter_value_t<O>,
std::iter_rvalue_reference_t<I>>
constexpr ranges::uninitialized_move_n_result<I, O>
operator()(I ifirst, std::iter_difference_t<I> count, O ofirst, S olast) const
{
auto iter = std::counted_iterator(std::move(ifirst), count);
auto ret = ranges::uninitialized_move(iter, std::default_sentinel, ofirst, olast);
return {std::move(ret.in).base(), ret.out};
}
};
inline constexpr uninitialized_move_n_fn uninitialized_move_n{};
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Example
Run this code
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <memory>
#include <string>
void print(auto rem, auto first, auto last)
{
for (std::cout << rem; first != last; ++first)
std::cout << std::quoted(*first) << ' ';
std::cout << '\n';
}
int main()
{
std::string in[]{ "No", "Diagnostic", "Required", };
print("initially, in: ", std::begin(in), std::end(in));
if (constexpr auto sz = std::size(in);
void* out = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz)
)
{
try
{
auto first{static_cast<std::string*>(out)};
auto last{first + sz};
std::ranges::uninitialized_move_n(std::begin(in), sz, first, last);
print("after move, in: ", std::begin(in), std::end(in));
print("after move, out: ", first, last);
std::ranges::destroy(first, last);
}
catch (...)
{
std::cout << "Exception!\n";
}
std::free(out);
}
}
Possible output:
initially, in: "No" "Diagnostic" "Required"
after move, in: "" "" ""
after move, out: "No" "Diagnostic" "Required"
See also
(C++20) |
moves a range of objects to an uninitialized area of memory (algorithm function object) |
(C++17) |
moves a number of objects to an uninitialized area of memory (function template) |