< cpp‎ | memory
Dynamic memory management
Uninitialized storage
Garbage collection support
C Library
Low level memory management
Defined in header <memory>
template< class ForwardIt >
void uninitialized_default_construct( ForwardIt first, ForwardIt last);
(1) (since C++17)
template< class ExecutionPolicy, class ForwardIt >
void uninitialized_default_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 default-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 true


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



Linear in the distance between first and last


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_default_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);


See also

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