std::uninitialized_value_construct
Defined in header <memory> | ||
---|---|---|
template< class ForwardIt >
void uninitialized_value_construct( ForwardIt first, ForwardIt last);
| (1) | (since C++17) |
template< class ExecutionPolicy, class ForwardIt >
void uninitialized_value_construct( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last );
| (2) | (since C++17) |
1) Constructs objects of type
typename iterator_traits<ForwardIt>::value_type
in the uninitialized storage designated by the range [first, last)
by value-initialization, as if by for (; first != last; ++first)
::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, last | - | the range of the 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
(none).
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 otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Possible implementation
template<class ForwardIt>
void uninitialized_value_construct(ForwardIt first, ForwardIt last)
{
using Value = typename std::iterator_traits<ForwardIt>::value_type;
ForwardIt current = first;
try {
for (; current != last; ++current) {
::new (static_cast<void*>(std::addressof(*current))) Value();
}
} 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 start and a count (function template) |
(C++17) | constructs objects by default-initialization in an uninitialized area of memory, defined by a range (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