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


std::destroy_n - std::destroy_n


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)

2) Same as (1), but executed according to policy. This overload does not participate
in overload resolution unless
(until C++20)
(since C++20) is true.


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

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)).


Linear in n.


The overload with a template parameter named ExecutionPolicy reports errors as

* 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)
return first;


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);


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)