std::uninitialized_value_construct_n
Defined in header <memory> | ||
---|---|---|
template< class ForwardIt, class Size >
ForwardIt uninitialized_value_construct_n( ForwardIt first, Size n );
| (1) | (since C++17) |
template< class ExecutionPolicy, class ForwardIt, class Size >
ForwardIt uninitialized_value_construct_n( ExecutionPolicy&& policy, ForwardIt first, Size n );
| (2) | (since C++17) |
1) Constructs
n
objects of type typename iterator_traits<ForwardIt>::value_type
in the uninitialized storage starting at first
by value-initialization, as if by for (; n > 0; (void) ++first, --n)
::new (static_cast<void*>(std::addressof(*first)))
typename std::iterator_traits<ForwardIt>::value_type();
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>>
is trueParameters
first | - | the beginning of the range of elements to initialize |
n | - | the number of elements to initialize |
policy | - | the execution policy to use. See execution policy for details. |
Type requirements | ||
-ForwardIt must meet the requirements of LegacyForwardIterator. |
||
-No increment, assignment, comparison, or indirection through valid instances of ForwardIt may throw exceptions. |
Return value
The end of the range of objects (i.e., std::next(first, n)
).
Complexity
Linear in n
.
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 ForwardIt, class Size>
ForwardIt uninitialized_value_construct_n( ForwardIt first, Size n )
{
using T = typename std::iterator_traits<ForwardIt>::value_type;
ForwardIt current = first;
try {
for (; n > 0 ; (void) ++current, --n) {
::new (static_cast<void*>(std::addressof(*current))) T();
}
return current;
} catch (...) {
std::destroy(first, current);
throw;
}
} |
Example
See also
(C++17) | constructs objects by value-initialization in an uninitialized area of memory, defined by a range (function template) |
(C++17) | constructs objects by default-initialization in an uninitialized area of memory, defined by a start and a count (function template) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/memory/uninitialized_value_construct_n