std::ranges::destroy_n
From cppreference.com
| Defined in header <memory>
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| Call signature |
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template< /*nothrow-input-iterator*/ I >
requires std::destructible<std::iter_value_t<I>>
constexpr I destroy_n( I first, std::iter_difference_t<I> count ) noexcept;
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(1) | (since C++20) |
template< /*execution-policy*/ Ep, /*nothrow-random-access-iterator*/ I >
requires std::destructible<std::iter_value_t<I>>
I destroy_n( Ep&& policy, I first, std::iter_difference_t<I> count );
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(2) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of other exposition-only concepts, see this page.
1) Destroys elements in the target range
first + [0, count) as if by
return std::ranges::destroy(std::counted_iterator(first, count),
std::default_sentinel).base();
2) Same as (1), but executed according to
policy.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.
Parameters
| first | - | the beginning of the range of elements to destroy |
| count | - | the number of elements to destroy |
| policy | - | the execution policy to use |
Return value
As described above.
Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_parallel_algorithm |
202506L |
(C++26) | Parallel range algorithms |
Possible implementation
struct destroy_n_fn
{
template</*nothrow-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{};
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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) * 4];
for (int i = 0; i < 4; ++i)
new (buffer + sizeof(Tracer) * i) Tracer{i}; // manually construct objects
auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));
std::ranges::destroy_n(ptr, 4);
}
Output:
0 destructed
1 destructed
2 destructed
3 destructed
See also
(C++20) |
destroys an object at a given address (algorithm function object) |
(C++20) |
destroys a range of objects (algorithm function object) |
(C++17) |
destroys a number of objects in a range (function template) |