std::destroy_n

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

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

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

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

Parameters

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.

#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);
}

0 destructed
1 destructed
2 destructed
3 destructed
4 destructed
5 destructed
6 destructed
7 destructed

See also