std::ranges::uninitialized_copy_n, std::ranges::uninitialized_copy_n_result
| Defined in header <memory>
|
||
| Call signature |
||
template< std::input_iterator I, no-throw-input-iterator O, no-throw-sentinel-for<O> S > |
(1) | (since C++20) (constexpr since C++26) |
| Helper types |
||
| template< class I, class O > using uninitialized_copy_n_result = ranges::in_out_result<I, O>; |
(2) | (since C++20) |
Let N be ranges::min(count, ranges::distance(ofirst, olast)).
Copies N elements from the range beginning at ifirst to an uninitialized memory area [ofirst, olast) as if by
auto 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.
Parameters
| ifirst | - | the beginning of the range of elements to copy from |
| count | - | the number of elements to copy |
| ofirst, olast | - | iterator-sentinel pair denoting the destination range |
Return value
As described above.
Complexity
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_copy_n, by using e.g. ranges::copy_n, if the value type of the output range is TrivialType.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_raw_memory_algorithms |
202411L |
(C++26) | constexpr for specialized memory algorithms, (1) |
Possible implementation
struct uninitialized_copy_n_fn { template<std::input_iterator I, no-throw-input-iterator O, no-throw-sentinel-for<O> S> requires std::constructible_from<std::iter_value_t<O>, std::iter_reference_t<I>> constexpr ranges::uninitialized_copy_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_copy(iter, std::default_sentinel, ofirst, olast); return {std::move(ret.in).base(), ret.out}; } }; inline constexpr uninitialized_copy_n_fn uninitialized_copy_n{}; |
Example
#include <iomanip> #include <iostream> #include <memory> #include <string> 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"};See also
| (C++20) |
copies a range of objects to an uninitialized area of memory (algorithm function object) |
| (C++11) |
copies a number of objects to an uninitialized area of memory (function template) |