std::uninitialized_copy() algorithm
- od C++17
- do C++17
// (1)
template< class InputIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy( InputIt first, InputIt last, NoThrowForwardIt d_first );
// (2)
template< class ExecutionPolicy, class ForwardIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last,
NoThrowForwardIt d_first );
// (1)
template< class InputIt, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy( InputIt first, InputIt last, NoThrowForwardIt d_first );
-
(1) Copies elements from the range [
first
;last
) to an uninitialized memory area beginning atd_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 */
is- od C++20
- od C++11
- do C++11
voidify(e)
static_cast<void*>(std::addressof(e))
static_cast<void*>(&e)
uwagaIf an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.
Undefined BehaviourIf d_first + [0
,std::distance(first, last)
) overlaps with [first
;last
), the behavior is undefined. (od C++20) -
(2) Same as (1), but executed according to
policy
.
These overloads participate in overload resolution only if
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(do C++20) std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(od C++20) is true
.
Parameters
first last | The range of 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 | LegacyInputIterator |
ForwardIt NoThrowForwardIt | 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. (do C++11)
Return value
Iterator to the element past the last element copied.
Complexity
Linear in the distance between first
and last
.
Exceptions
The overloads with a template parameter named ExecutionPolicy
report 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 none otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Possible implementation
uninitialized_copy (1)
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;
}
}
Examples
#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);
}
}
This_is_an_example_
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