# std::ranges::destroy_n

From cppreference.com
< cpp‎ | memory

Defined in header `<memory>` |  |
Call signature |  |
template< no-throw-input-iterator I > requires std::destructible<std::iter_value_t<I>> constexpr I destroy_n( I first, std::iter_difference_t<I> n ) noexcept; |  | (since C++20)

Destroys the n objects in the range starting at first, equivalent to

    return std::ranges::destroy(std::counted_iterator(first, n), std::default_sentinel).base();

The function-like entities described on this page are niebloids, that is:

- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

### Parameters

first | - | the beginning of the range of elements to destroy
n | - | the number of elements to destroy

### Return value

The end of the range of objects that has been destroyed.

### Complexity

Linear in n.

### Possible implementation

    struct destroy_n_fn
    {
        template<no-throw-input-iterator I>
            requires std::destructible<std::iter_value_t<I>>
        constexpr I operator()(I first, std::iter_difference_t<I> n) const noexcept
        {
            for (; n != 0; (void)++first, --n)
                std::ranges::destroy_at(std::addressof(*first));
            return first;
        }
    };

    inline constexpr destroy_n_fn destroy_n{};

### Example

The following example demonstrates how to use `ranges::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::ranges::destroy_n(ptr, 8);
    }

Output:

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

### See also

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

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