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std::ranges::uninitialized_move, std::ranges::uninitialized_move_result - cppreference.com

Call signature

Helper types

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

Copies

elements from

(using move semantics if supported) to an uninitialized memory area

as if by

for (; ifirst != ilast && ofirst != olast; ++ofirst, (void)++ifirst)
    ::new (voidify(*ofirst))
        std::remove_reference_t<std::iter_reference_t<O>>(ranges::iter_move(ifirst));
return {std::move(ifirst), ofirst};

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 [ifirst, ilast) that were already moved, are left in a valid but unspecified state.

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.

As described above.

Linear in \(\scriptsize N\)N.

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

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

struct uninitialized_move_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_rvalue_reference_t<I>>
    constexpr ranges::uninitialized_move_result<I, O>
        operator()(I ifirst, S1 ilast, O ofirst, S2 olast) const
    {
        using ValueType = std::remove_reference_t<std::iter_reference_t<O>>;
        O current{ofirst};
        try
        {
            for (; !(ifirst == ilast or current == olast); ++ifirst, ++current)
                ::new (static_cast<void*>(std::addressof(*current))))
                    ValueType(ranges::iter_move(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>,
                                         ranges::range_rvalue_reference_t<IR>>
    constexpr ranges::uninitialized_move_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_move_fn uninitialized_move{};

#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[]{"Home", "World"};
    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(std::begin(in), std::end(in), 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: "Home" "World"
after move, in: "" ""
after move, out: "Home" "World"

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

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