std::ranges::uninitialized_move, std::ranges::uninitialized_move_result - cppreference.com (original) (raw)

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

1. Copies \(\scriptsize N\)N elements from [ifirst, ilast) (using move semantics if supported) to an uninitialized memory area [ofirst, olast) as if by

for (; ifirst != ilast && ofirst != olast; ++ofirst, (void)++ifirst)
::new ([_voidify_](../voidify.html "cpp/memory/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.

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

Linear in \(\scriptsize N\)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, e.g. by using ranges::copy_n, if the value type of the output range is TrivialType.

[edit] Possible implementation

struct uninitialized_move_fn { template<std::input_iterator I, std::sentinel_for S1, no-throw-forward-iterator O, no-throw-sentinel-for S2> requires std::constructible_from<std::iter_value_t, std::iter_rvalue_reference_t> 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 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, ranges::range_rvalue_reference_t> constexpr ranges::uninitialized_move_result<ranges::borrowed_iterator_t, ranges::borrowed_iterator_t> 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{};

[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[]{"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"

[edit] Defect reports

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

[edit] See also