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std::destroy_n

Defined in header <memory>

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

template< class ForwardIt, class Size >
ForwardIt destroy_n( ForwardIt first, Size n );

(1)

(since C++17)

template< class ExecutionPolicy, class ForwardIt, class Size >
ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n );

(2)

(since C++17)

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.

#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

destroy (C++17)	destroys a range of objects (function template)
destroy_at (C++17)	destroys an object at a given address (function template)