std::uninitialized_copy_n
Defined in header <memory> |
||
---|---|---|
template< class InputIt, class Size, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy_n( InputIt first, Size count, NoThrowForwardIt d_first ); |
(1) | (since C++11) |
template< class ExecutionPolicy, class ForwardIt, class Size, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy_n( ExecutionPolicy&& policy, ForwardIt first, Size count, NoThrowForwardIt d_first ); |
(2) | (since C++17) |
1) Copies
count
elements from a range beginning at
first
to an uninitialized memory area beginning at
d_first
as if by
for ( ; n > 0; ++d_first, (void) ++first, --n) ::new (/*VOIDIFY*/(*d_first)) typename std::iterator_traits<NoThrowForwardIt>::value_type(*first);
where /*VOIDIFY*/(e)
is:
static_cast<void*>(std::addressof(e)) |
(until C++20) |
const_cast<void*>(static_cast<const volatile void*>(std::addressof(e))) |
(since C++20) |
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 | - | the beginning of the range of the elements to copy |
count | - | the number 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 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. |
Return value
Iterator to the element past the last element copied.
Complexity
Linear in count
.
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 otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Possible implementation
template<class InputIt, class Size, class NoThrowForwardIt> NoThrowForwardIt uninitialized_copy_n(InputIt first, Size count, NoThrowForwardIt d_first) { using T = typename std::iterator_traits<NoThrowForwardIt>::value_type; NoThrowForwardIt current = d_first; try { for (; count > 0; ++first, (void) ++current, --count) { ::new (const_cast<void*>(static_cast<const volatile void*>( std::addressof(*current)))) T(*first); } } catch (...) { for (; d_first != current; ++d_first) { d_first->~T(); } throw; } return current; } |
Example
#include <algorithm> #include <iostream> #include <memory> #include <string> #include <tuple> #include <vector> int main() { std::vector<std::string> v = {"This", "is", "an", "example"}; std::string* p; std::size_t sz; std::tie(p, sz) = std::get_temporary_buffer<std::string>(v.size()); sz = std::min(sz, v.size()); std::uninitialized_copy_n(v.begin(), sz, p); for (std::string* i = p; i != p+sz; ++i) { std::cout << *i << ' '; i->~basic_string<char>(); } std::return_temporary_buffer(p); }
Output:
This is an example
See also
copies a range of objects to an uninitialized area of memory (function template) |
|
(C++20)
|
copies a number of objects to an uninitialized area of memory (niebloid) |
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