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

std::uninitialized_copy_n - cppreference.com

template< class InputIt, class Size, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy_n( InputIt first, Size count, NoThrowForwardIt d_first ); (1) (since C++11)
(constexpr since C++26) template< class ExecutionPolicy, class ForwardIt, class Size, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy_n( ExecutionPolicy&& policy, ForwardIt first, Size count, NoThrowForwardIt d_first ); (2) (since C++17) 1)

Copies

count

elements from a range beginning at

first

to an uninitialized memory area beginning at

d_first

as if by

for (; count > 0; ++d_first, (void) ++first, --count) ::new (voidify(*d_first)) typename std::iterator_traits<NoThrowForwardIt>::value_type(*first);

If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.

2) Same as (1), but executed according to policy.

This overload participates in overload resolution only if all following conditions are satisfied:

If d_first + [â0â, count) overlaps with first + [â0â, count), the behavior is undefined.

(since C++20) [edit] Parameters first - the beginning of the range of the elements to copy count - the number of elements to copy d_first - the beginning of the destination range policy - the execution policy to use Type requirements -InputIt must meet the requirements of LegacyInputIterator. -ForwardIt must meet the requirements of LegacyForwardIterator. -NoThrowForwardIt must meet the requirements of LegacyForwardIterator. -No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt may throw exceptions. [edit] Return value

Iterator to the element past the last element copied.

[edit] Complexity

Linear in count.

[edit] Exceptions

The overload with a template parameter named ExecutionPolicy reports errors as follows:

If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
If the algorithm fails to allocate memory, std::bad_alloc is thrown.

[edit] Notes [edit] Possible implementation

template<class InputIt, class Size, class NoThrowForwardIt>
constexpr NoThrowForwardIt uninitialized_copy_n(InputIt first, Size count,
                                                NoThrowForwardIt d_first)
{
    using T = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = d_first;
    try
    {
        for (; count > 0; ++first, (void) ++current, --count)
            ::new (static_cast<void*>(std::addressof(*current))) T(*first);
    }
    catch (...)
    {
        for (; d_first != current; ++d_first)
            d_first->~T();
        throw;
    }
    return current;
}

[edit] Example [edit] Defect reports

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

DR Applied to Behavior as published Correct behavior LWG 2133 C++98 the effect description used a for loop with the iteration
expression ++d_first, ++first, --count, which
results in argument-dependent lookups of operator, discards the value
of one operand to
disable those ADLs LWG 2433 C++11 this algorithm might be hijacked by overloaded operator& uses std::addressof LWG 3870 C++20 this algorithm might create objects on a const storage kept disallowed [edit] See also

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