std::destroy_n (3) - Linux Man Pages

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

See also


destroy destroys a range of objects
           (function template)
(C++17)


destroy_at destroys an object at a given address
           (function template)
(C++17)