std:: uninitialized_copy

From cppreference.com

Defined in header `<memory>`
template < class InputIt, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy ( InputIt first, InputIt last, NoThrowForwardIt d_first ) ;	(1)
template < class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy ( ExecutionPolicy && policy, ForwardIt first, ForwardIt last, NoThrowForwardIt 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 ( /* VOIDIFY */ ( * d_first ) )
typename std:: iterator_traits < NoThrowForwardIt > :: value_type ( * first ) ;

where /* VOIDIFY */ ( e ) is:

static_cast < void * > ( & e )	(until C++11)
static_cast < void * > ( std:: addressof ( e ) )	(since C++11)

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

If d_first + [ 0 , std:: distance ( first, last ) ) overlaps with [ first , last ) , the behavior is undefined.

(since C++20)

2) Same as (1) , but executed according to policy . This overload participates in overload resolution only if

std:: is_execution_policy_v < std:: decay_t < ExecutionPolicy >> is true .	(until C++20)
std:: is_execution_policy_v < std:: remove_cvref_t < ExecutionPolicy >> is true .	(since C++20)

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 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. Applying & * to a `NoThrowForwardIt` value must yield a pointer to its value type. (until C++11)

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

Example

Run this code

#include <cstdlib>
#include <iostream>
#include <memory>
#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::cout << '\n';
 
            std::destroy(first, last);
        }
        catch (...) {}
        std::free(pbuf);
    }
}

Output:

This_is_an_example_

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 866	C++98	given `T` as the value type of `NoThrowForwardIt` , if T :: operator new exists, the program might be ill-formed	uses global replacement- new instead
LWG 2133	C++98	the effect description used a for loop with the iteration expression ++ d_first, ++ first , which results in an argument-dependent lookup of operator,	discards the value of one operand to disable that ADL
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

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External libraries

uninitialized_copy_n (C++11)	copies a number of objects to an uninitialized area of memory (function template)
ranges::uninitialized_copy (C++20)	copies a range of objects to an uninitialized area of memory (algorithm function object)