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std::destroy_n - cppreference.com

From cppreference.com

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)

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

See also