NAME¶

std::uninitialized_copy - std::uninitialized_copy

Synopsis¶

Defined in header <memory>
template< class InputIt, class NoThrowForwardIt >

NoThrowForwardIt uninitialized_copy( InputIt first, InputIt last, (1)

NoThrowForwardIt d_first );
template< class ExecutionPolicy, class ForwardIt, class
NoThrowForwardIt >

NoThrowForwardIt uninitialized_copy( ExecutionPolicy&& policy, (2) (since C++17)
ForwardIt first, ForwardIt
last,

NoThrowForwardIt d_first );

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 (since C++20)
[first, last), the behavior is undefined.

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
given T as the value type of
LWG 866 C++98 NoThrowForwardIt, if uses global replacement-
T::operator new exists, the program new instead
might be ill-formed
the effect description used a for loop
with the iteration discards the value
LWG 2133 C++98 expression ++d_first, ++first, which of one operand
results to disable that ADL
in an argument-dependent lookup of
operator,
LWG 2433 C++11 this algorithm might be hijacked by uses std::addressof
overloaded operator&
LWG 3870 C++20 this algorithm might create objects on kept disallowed
a const storage

See also¶

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