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std::uninitialized_copy

Defined in header <memory>

Defined in header `<memory>`
template< class InputIt, class ForwardIt > ForwardIt uninitialized_copy( InputIt first, InputIt last, ForwardIt d_first );	(1)
template< class ExecutionPolicy, class InputIt, class ForwardIt > ForwardIt uninitialized_copy( ExecutionPolicy&& policy, InputIt first, InputIt last, ForwardIt d_first );	(2)	(since C++17)

template< class InputIt, class ForwardIt >
ForwardIt uninitialized_copy( InputIt first, InputIt last, ForwardIt d_first );

(1)

template< class ExecutionPolicy, class InputIt, class ForwardIt >
ForwardIt uninitialized_copy( ExecutionPolicy&& policy, InputIt first, InputIt last, ForwardIt d_first );

(2)

(since C++17)

1) Copies elements from the range [first, last) to an uninitialized memory area beginning at d_first as if by

for (; first != last; ++d_first, (void) ++first)
   ::new (static_cast<void*>(std::addressof(*d_first)))
      typename std::iterator_traits<ForwardIt>::value_type(*first);

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

2) Same as (1), but executed according to policy. This overload does not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

Parameters

first, last	-	the range of the elements to copy
d_first	-	the beginning of the destination range
policy	-	the execution policy to use. See execution policy for details.
Type requirements
-`InputIt` must meet the requirements of InputIterator.
-`ForwardIt` must meet the requirements of ForwardIterator.
-No increment, assignment, comparison, or indirection through valid instances of `ForwardIt` may throw exceptions.

Return value

Iterator to the element past the last element copied.

Complexity

Linear in the distance between first and last.

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 three 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.

Possible implementation

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

Example

#include <iostream>
#include <memory>
#include <cstdlib>
#include <string>
 
int main()
{
    const char *v[] = {"This", "is", "an", "example"};
 
    auto sz = std::size(v);
 
    if(void *pbuf = std::aligned_alloc(alignof(std::string), sizeof(std::string) * sz))
    {
        try
        {
            auto first = static_cast<std::string*>(pbuf);
            auto last = std::uninitialized_copy(std::begin(v), std::end(v), first);
 
            for (auto it = first; it != last; ++it)
                std::cout << *it << '_';
 
            std::destroy(first, last);
        }
        catch(...) {}
        std::free(pbuf);
    }
}

Output:

This_is_an_example_