std::uninitialized_copy

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)

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)

[edit] Return value

Iterator to the element past the last element copied.

[edit] Complexity

Linear in the distance between first and last.

[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] 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;
    }
}

[edit] 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_

[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 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

[edit] See also

uninitialized_copy_n (C++11)	copies a number of objects to an uninitialized area of memory (function template) [edit]
ranges::uninitialized_copy (C++20)	copies a range of objects to an uninitialized area of memory (niebloid)[edit]

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std::uninitialized_copy

Contents

[edit] Parameters