NAME

std::ranges::destroy_n - std::ranges::destroy_n

Synopsis

Defined in header <memory>
Call signature
template< no-throw-input-iterator I >

requires std::destructible<std::iter_value_t<I>> (since C++20)

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 may not be specified when calling any of them.
* None of them is visible to argument-dependent lookup.
* When one of them is found by normal unqualified lookup for the name to the left
of the function-call operator, it inhibits argument-dependent lookup.

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 <memory>
#include <new>
#include <iostream>

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