< cpp‎ | memory
Dynamic memory management
Uninitialized storage
(deprecated since c++17)
(deprecated since c++17)
(deprecated since c++17)
Garbage collection support
C Library
Low level memory management
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 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


[edit] Parameters

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 ForwardIterator.
No increment, assignment, comparison, or indirection through valid instances of ForwardIt may throw exceptions.

[edit] Return value

The end of the range of objects (i.e., std::next(first, n)).

[edit] Complexity

Linear in n.

[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 three 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.

[edit] Possible implementation

template<class ForwardIt, class Size>
ForwardIt uninitialized_value_construct_n( ForwardIt first, Size n )
    typedef typename std::iterator_traits<ForwardIt>::value_type Value;
    ForwardIt current = first;
    try {
        for (; n > 0 ; (void) ++current, --n) {
            ::new (static_cast<void*>(std::addressof(*current))) Value();
        return current;
    }  catch (...) {
        for (; first != current; ++first) {

[edit] Example

[edit] See also

constructs objects by value-initialization in an uninitialized area of memory, defined by a range
(function template) [edit]
constructs objects by default-initialization in an uninitialized area of memory, defined by a start and a count
(function template) [edit]