std::ranges::destroy_n
From cppreference.com
| Defined in header <memory>
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| Call signature |
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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;
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(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 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 |
| 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{};
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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