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Difference between revisions of "cpp/memory/uninitialized value construct"

From cppreference.com
< cpp‎ | memory
m (Text replace - "par req concept" to "par req named")
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             ::new (static_cast<void*>(std::addressof(*current))) Value();
 
             ::new (static_cast<void*>(std::addressof(*current))) Value();
 
         }
 
         }
−
     } catch (...) {
+
     } catch (...) {
 
         for (; first != current; ++first) {
 
         for (; first != current; ++first) {
 
             first->~Value();
 
             first->~Value();

Revision as of 17:10, 26 June 2018

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Dynamic memory management
Uninitialized memory algorithms
(C++17)
(C++17)
uninitialized_value_construct
(C++17)
(C++17)
(C++17)
(C++20)
Constrained uninitialized memory algorithms
Allocators
Garbage collection support
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)



 
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 function has no effects.
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 true

Contents

Parameters

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 other ExecutionPolicy, 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)
{
    typedef typename std::iterator_traits<ForwardIt>::value_type Value;
    ForwardIt current = first;
    try {
        for (; current != last; ++current) {
            ::new (static_cast<void*>(std::addressof(*current))) Value();
        }
    } catch (...) {
        for (; first != current; ++first) {
            first->~Value();
        }
        throw;
    }
}

Example

This section is incomplete
Reason: no 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) [edit]
(C++17)
 constructs objects by default-initialization in an uninitialized area of memory, defined by a range
(function template) [edit]
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