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    std::destroy_n

    From cppreference.com
     
    C++
     
    Memory management library
    (exposition only*)
    Allocators
    Uninitialized memory algorithms
    Constrained uninitialized memory algorithms
    Memory resources
    Uninitialized storage (until C++20)
    (until C++20*)
    (until C++20*)
    (until C++20*)

    Garbage collector support (until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
    (C++11)(until C++23)
     
    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 all following conditions are satisfied:
    See More

    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
    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

    (C++17)
    		 destroys a range of objects
    (function template) [edit]
    (C++17)
    		 destroys an object at a given address
    (function template) [edit]
    (C++20)
    		 destroys a number of objects in a range
    (algorithm function object)[edit]