std::destroy_n(3) | C++ Standard Libary | std::destroy_n(3) |
NAME¶
std::destroy_n - std::destroy_n
Synopsis¶
Defined in header <memory>
template< class ForwardIt, class Size > (since C++17)
ForwardIt destroy_n( ForwardIt first, Size n ); (until C++20)
template< class ForwardIt, class Size > (since C++20)
constexpr ForwardIt destroy_n( ForwardIt first, Size n ); (1)
template< class ExecutionPolicy, class ForwardIt, class Size >
ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt (2)
(since C++17)
first, Size n );
1) Destroys the n objects in the range starting at first, as if by
for (; n > 0; (void) ++first, --n)
std::destroy_at(std::addressof(*first));
2) Same as (1), but executed according to policy. This overload
participates in
overload resolution only if
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is
true. (until
C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
is true. (since
C++20)
Parameters¶
first - the beginning of the range of elements to destroy
n - the number of elements to destroy
policy - the execution policy to use. See execution policy for
details.
Type requirements¶
-
ForwardIt must meet the requirements of LegacyForwardIterator.
-
No increment, assignment, comparison, or indirection through valid instances
of
ForwardIt may throw exceptions.
Return value¶
The end of the range of objects that has been destroyed (i.e., std::next(first, n)).
Complexity¶
Linear in n.
Exceptions¶
The overload with a template parameter named ExecutionPolicy
reports errors as
follows:
* If execution of a function invoked as part of the algorithm throws an
exception
and ExecutionPolicy is one of the standard policies, std::terminate is
called.
For any other ExecutionPolicy, the behavior is implementation-defined.
* If the algorithm fails to allocate memory, std::bad_alloc is thrown.
Possible implementation¶
template<class ForwardIt, class Size>
constexpr // since C++20
ForwardIt destroy_n(ForwardIt first, Size n)
{
for (; n > 0; (void) ++first, --n)
std::destroy_at(std::addressof(*first));
return first;
}
Example¶
The following example demonstrates how to use 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::destroy_n(ptr, 8);
}
Output:¶
0 destructed
1 destructed
2 destructed
3 destructed
4 destructed
5 destructed
6 destructed
7 destructed
See also¶
destroy destroys a range of objects
(C++17) (function template)
destroy_at destroys an object at a given address
(C++17) (function template)
ranges::destroy_n destroys a number of objects in a range
(C++20) (niebloid)
2024.06.10 | http://cppreference.com |