std::destroy_n

 

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Defined in header <memory>
	(1)
template< class ForwardIt, class Size > ForwardIt destroy_n( ForwardIt first, Size n );			(since C++17) (until C++20)
template< class ForwardIt, class Size > constexpr ForwardIt destroy_n( ForwardIt first, Size n );			(since C++20)
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 participates 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 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> 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 (C++17)	destroys a range of objects (function template)
destroy_at (C++17)	destroys an object at a given address (function template)
ranges::destroy_n (C++20)	destroys a number of objects in a range (niebloid)