std::ranges::uninitialized_move_n, std::ranges::uninitialized_move_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 (using move semantics if supported) to an uninitialized memory area [ofirst, olast) as if byauto 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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Exceptions
• 5 Notes
• 6 Possible implementation
• 7 Example
• 8 Defect reports
• 9 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_move_n, e.g. by using ranges::copy_n, if the value type of the output range is TrivialType.

[edit] Possible implementation

struct uninitialized_move_n_fn { template<std::input_iterator I, no-throw-forward-iterator O, no-throw-sentinel-for S> requires std::constructible_from<std::iter_value_t, std::iter_rvalue_reference_t> constexpr ranges::uninitialized_move_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_move(iter, std::default_sentinel, ofirst, olast); return {std::move(ret.in).base(), ret.out}; } };   inline constexpr uninitialized_move_n_fn uninitialized_move_n{};

[edit] Example

#include #include #include #include #include   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"

[edit] Defect reports

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

[edit] See also