std::ranges::destroy_n
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ranges::destroy_n
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Defined in header
<memory>
Call signature
template< no-throw-input-iterator I >
(since C++20)
requires std::destructible <std::iter_value_t <I>>
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 algorithm function objects (informally known as 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.
[edit] Parameters
first
-
the beginning of the range of elements to destroy
n
-
the number of elements to destroy
[edit] Return value
The end of the range of objects that has been destroyed.
[edit] Complexity
Linear in n.
[edit] 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{};
[edit] 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