std::destroy_n (3) - Linux Manuals

std::destroy_n: std::destroy_n

NAME

std::destroy_n - std::destroy_n

Synopsis

Defined in header <memory>
template< class ForwardIt, class Size > (1) (since C++17)
ForwardIt destroy_n( ForwardIt first, Size n );
template< class ExecutionPolicy, class ForwardIt, class Size > (2) (since C++17)
ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n );

1) Destroys the n objects in the range starting at first, as if by

  for (; n > 0; (void) ++first, --n)
    std::destroy_at(std::addressof(*first));

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

Parameters

first - the beginning of the range of elements to destroy
n - the number of elements to destroy
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 that has been destroyed (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 other ExecutionPolicy, 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 destroy_n( ForwardIt first, Size n )
  {
    for (; n > 0; (void) ++first, --n)
      std::destroy_at(std::addressof(*first));
    return first;
  }

Example

The following example demonstrates how to use destroy_n to destroy a contiguous sequence of elements.
// Run this code

  #include <memory>
  #include <new>
  #include <iostream>

  struct Tracer {
      int value;
      ~Tracer() { std::cout << value << " destructed\n"; }
  };

  int main()
  {
      alignas(Tracer) unsigned char buffer[sizeof(Tracer) * 8];

      for (int i = 0; i < 8; ++i)
          new(buffer + sizeof(Tracer) * i) Tracer{i}; //manually construct objects

      auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));

      std::destroy_n(ptr, 8);

  }

Output:

  0 destructed
  1 destructed
  2 destructed
  3 destructed
  4 destructed
  5 destructed
  6 destructed
  7 destructed