std::ranges::uninitialized_copy_n, std::ranges::uninitialized_copy_n_result - cppreference.com (original) (raw)

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

Copies \(\scriptsize N\)N elements from the range beginning at ifirst to an uninitialized memory area [ofirst, olast) as if byauto ret = ranges::uninitialized_copy(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, the objects already constructed are destroyed in an unspecified order.

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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Notes
• 6 Possible implementation
• 7 Example
• 8 See also

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

[edit] Possible implementation

struct uninitialized_copy_n_fn { template<std::input_iterator I, no-throw-input-iterator O, no-throw-sentinel-for S> requires std::constructible_from<std::iter_value_t, std::iter_reference_t> constexpr ranges::uninitialized_copy_n_result<I, O> operator()(I ifirst, std::iter_difference_t count, O ofirst, S olast) const { auto iter = std::counted_iterator(std::move(ifirst), count); auto ret = ranges::uninitialized_copy(iter, std::default_sentinel, ofirst, olast); return {std::move(ret.in).base(), ret.out}; } };   inline constexpr uninitialized_copy_n_fn uninitialized_copy_n{};

[edit] Example

#include #include #include #include   int main() { const char* stars[]{"Procyon", "Spica", "Pollux", "Deneb", "Polaris"};   constexpr int n{4}; alignas(alignof(std::string)) char out[n * sizeof(std::string)];   try { auto first{reinterpret_cast<std::string*>(out)}; auto last{first + n}; auto ret{std::ranges::uninitialized_copy_n(std::begin(stars), n, first, last)};   std::cout << '{'; for (auto it{first}; it != ret.out; ++it) std::cout << (it == first ? "" : ", ") << std::quoted(*it); std::cout << "};\n";   std::ranges::destroy(first, last); } catch (...) { std::cout << "uninitialized_copy_n exception\n"; } }

Output:

{"Procyon", "Spica", "Pollux", "Deneb"};

[edit] See also