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)
(until C++20)
const_cast<void*>(static_cast<const volatile (since C++20)
void*>(std::addressof(e)))

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. This overload does not participate
in overload resolution unless
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20) 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 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 (const_cast<void*>(static_cast<const volatile void*>(
std::addressof(*current)))) T(*first);
}
return current;
} catch (...) {
for (; d_first != current; ++d_first) {
d_first->~T();
}
throw;
} }

Example¶

// Run this code

#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::cout << '\n';

std::destroy(first, last);
}
catch(...) {}
std::free(pbuf);
}
}

Output:¶

This_is_an_example_

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)