std::ranges::uninitialized_move_n, std::ranges::uninitialized_move_n_result

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

Copies \(\scriptsize N\)N elements from the range beginning at ifirst (using move semantics if supported) to an uninitialized memory area [ofirst, olast) 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.

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.

[edit] Parameters

[edit] Return value

As described above.

[edit] Complexity

\(\scriptsize\mathcal{O}(N)\)O(N).

[edit] Exceptions

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

[edit] Notes

An implementation may improve the efficiency of the ranges::uninitialized_move_n, e.g. by using ranges::copy_n , if the value type of the output range is TrivialType.

[edit] Possible implementation

struct uninitialized_move_n_fn
{
 template<std::input_iterator I,
 no-throw-forward-iterator O, no-throw-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{};

[edit] Example

#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);
 }
}

initially, in: "No" "Diagnostic" "Required"
after move, in: "" "" ""
after move, out: "No" "Diagnostic" "Required"

[edit] Defect reports

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

[edit] See also

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