std::uninitialized_copy_n

Defined in header `<memory>`
template< class InputIt, class Size, class ForwardIt > ForwardIt uninitialized_copy_n( InputIt first, Size count, ForwardIt d_first);		(since C++11)

Copies count elements from a range beginning at first to an uninitialized memory area beginning at d_first as if by.

for ( ; n > 0; ++d_first, (void) ++first, --n)
   ::new (static_cast<void*>(std::addressof(*d_first)))
      typename iterator_traits<ForwardIterator>::value_type(*first);

If an exception is thrown during the initialization, the function has no effects.

Parameters

first	-	the beginning of the range of the elements to copy
d_first	-	the beginning of the destination range
Type requirements
- `InputIt` must meet the requirements of `InputIterator`.
- `ForwardIt` must meet the requirements of `ForwardIterator`.

Return value

Iterator to the element past the last element copied.

Complexity

Linear in count.

Possible implementation

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

Example

#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <tuple>
#include <vector>
 
int main()
{
    std::vector<std::string> v = {"This", "is", "an", "example"};
 
    std::string* p;
    std::size_t sz;
    std::tie(p, sz)  = std::get_temporary_buffer<std::string>(v.size());
    sz = std::min(sz, v.size());
 
    std::uninitialized_copy_n(v.begin(), sz, p);
 
    for (std::string* i = p; i != p+sz; ++i) {
        std::cout << *i << ' ';
        i->~basic_string<char>();
    }
    std::return_temporary_buffer(p);
}

Output:

This is an example

uninitialized_copy	copies a range of objects to an uninitialized area of memory (function template)
std::experimental::parallel::uninitialized_copy_n (parallelism TS)	parallelized version of `std::uninitialized_copy_n` (function template)