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std::destroy_n(3)	       C++ Standard Libary	       std::destroy_n(3)

NAME
     std::destroy_n - std::destroy_n

Synopsis
	Defined in header <memory>
	template<	 class	      ForwardIt,	class	    Size       >
     (since C++17)
	ForwardIt     destroy_n(     ForwardIt	   first,     Size     n      );
     (until C++20)
	template<	 class	      ForwardIt,	class	    Size       >
     (since C++20)
	constexpr ForwardIt destroy_n( ForwardIt first, Size n );      (1)
	template< class ExecutionPolicy, class ForwardIt, class Size >
	ForwardIt destroy_n( ExecutionPolicy&& policy,	ForwardIt	     (2)
     (since C++17)
	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 partici-
     pates in
	overload resolution only if

	std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>    is    true.
     (until
										  C++20)
	std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>      is
     true. (since
										  C++20)

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 in-
     stances 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 er-
     rors 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-de-
     fined.
	  * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation
	template<class ForwardIt, class Size>
	constexpr // since C++20
	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 <iostream>
      #include <memory>
      #include <new>

      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
	(C++17) 	  (function template)
	destroy_at	  destroys an object at a given address
	(C++17) 	  (function template)
	ranges::destroy_n destroys a number of objects in a range
	(C++20) 	  (niebloid)

http://cppreference.com 	   2024.06.10		       std::destroy_n(3)
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