std::destroy_n
From cppreference.com
| Defined in header <memory>
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| (1) | ||
| template< class ForwardIt, class Size > ForwardIt destroy_n( ForwardIt first, Size n ); |
(since C++17) (until C++20) |
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| template< class ForwardIt, class Size > constexpr ForwardIt destroy_n( ForwardIt first, Size n ); |
(since C++20) | |
| template< class ExecutionPolicy, class ForwardIt, class Size > ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n ); |
(2) | (since C++17) |
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 does not participate in overload resolution unless
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std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true. |
(until C++20) |
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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.
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-No increment, assignment, comparison, or indirection through valid instances of ForwardIt may throw exceptions.
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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
ExecutionPolicyis one of the standard policies, std::terminate is called. For any otherExecutionPolicy, 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
| (C++17) |
destroys a range of objects (function template) |
| (C++17) |
destroys an object at a given address (function template) |
| (C++20) |
destroys a number of objects in a range (niebloid) |