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.

Parameters

Return value

Iterator to the element past the last element copied.

Complexity

Linear in count.

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.

Notes

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;
}

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::cout << '\n';
    
    std::return_temporary_buffer(p);
}

Defect reports

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

See also