std::ranges::destroy_n

 

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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)