std::ranges::destroy_n

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;

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

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.

#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);
}

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

See also