std::uninitialized_copy_n
Defined in header <memory>
|
||
template< class InputIt, class Size, class NoThrowForwardIt > NoThrowForwardIt uninitialized_copy_n( InputIt first, Size count, |
(1) | (since C++11) |
template< class ExecutionPolicy, class ForwardIt, class Size, class NoThrowForwardIt > |
(2) | (since C++17) |
for (; n > 0; ++d_first, (void) ++first, --n)
::new (static_cast<void*>(std::addressof(*d_first)))
typename std::iterator_traits<NoThrowForwardIt>::value_type(*first);
If d_first |
(since C++20) |
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) |
Contents |
[edit] 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.
|
[edit] Return value
Iterator to the element past the last element copied.
[edit] Complexity
Linear in count.
[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 otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory, std::bad_alloc is thrown.
[edit] 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 (static_cast<void*>(std::addressof(*current))) T(*first); } catch (...) { for (; d_first != current; ++d_first) d_first->~T(); throw; } return current; } |
[edit] 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::cout << '\n'; std::return_temporary_buffer(p); }
Possible 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 2133 | C++98 | the effect description used a for loop with the iteration expression ++d_first, ++first, --n, which results in argument-dependent lookups of operator, |
discards the value of one operand to disable those ADLs |
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
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 (algorithm function object) |