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.

Parameters

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 the ranges::uninitialized_move_n , e.g. by using ranges::copy_n , if the value type of the output range is TrivialType .

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{};

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"

Defect reports

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

See also