Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://en.cppreference.com/w/cpp/language/../memory/ranges/uninitialized_move_n.html below:

std::ranges::uninitialized_move_n, std::ranges::uninitialized_move_n_result - cppreference.com

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.

As described above.

\(\scriptsize\mathcal{O}(N)\)𝓞(N).

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

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.

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{};

#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"

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

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4