std::destroy_n

Defined in header <memory>

Defined in header `<memory>`
template< class ForwardIt, class Size > ForwardIt destroy_n( ForwardIt first, Size count );	(1)	(since C++17) (constexpr since C++20)
template< class ExecutionPolicy, class ForwardIt, class Size > ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size count );	(2)	(since C++17)

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

(1)

(since C++17)
(constexpr since C++20)

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

(2)

(since C++17)

1) Destroys the first count elements in the target range [first, last) as if by

for (; count > 0; (void) ++first, --count)
    std::destroy_at(std::addressof(*first));
return first;

2) Same as (1), but executed according to policy.

This overload participates in overload resolution only if the value of the following expression is true:

`std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>`	(until C++20)
`std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>`	(since C++20)

Parameters

first	-	the beginning of the range of elements to destroy
count	-	the number of elements to destroy
policy	-	the execution policy to use
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

As described above.

Exceptions

2) During the execution process:

If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

Example

Demonstrates how to use destroy_n to destroy a contiguous sequence of elements.

#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) * 4];
    
    for (int i = 0; i < 4; ++i)
        new (buffer + sizeof(Tracer) * i) Tracer{i}; // manually construct objects

    auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));

    std::destroy_n(ptr, 4);
}

Output:

0 destructed
1 destructed
2 destructed
3 destructed

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

std::destroy_n

Parameters

Return value

Exceptions

Example

See also