std::destroy_n
From cppreference.com
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Memory management library
(exposition only*)
(C++11)
(C++23)
(C++11)
(C++17)
(C++11)
(C++11)
(C++20)
(C++20)
(C++17)
(C++11)
(C++17)
(C++20)
(C++17)
(C++17)
(C++17)
(C++17)
destroy_n
(C++17)
(C++17)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
(C++17)
Uninitialized storage (until C++20)
(until C++20*)
(until C++20*)
(until C++20*)
Garbage collector support (until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)
(C++11)
(C++17)
(C++20)
(C++17)
(C++11)
(C++11)
(C++11)
(until C++17*)
(C++11)
(C++17)
(C++26)
(C++26)
(C++11)
(C++11)
(C++11)
(C++23)
(C++23)
(C++11)
(C++20)
(C++11)
(C++11)
(C++20)
(C++26)
Defined in header
<memory>
(1)
template< class ForwardIt, class Size >
ForwardIt destroy_n( ForwardIt first, Size n );
(since C++17) ForwardIt destroy_n( ForwardIt first, Size n );
(until C++20)
template< class ForwardIt, class Size >
constexpr ForwardIt destroy_n( ForwardIt first, Size n );
(since C++20)
constexpr ForwardIt destroy_n( ForwardIt first, Size n );
template< class ExecutionPolicy, class ForwardIt, class Size >
ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n );
(2)
(since C++17)
ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt 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 all following conditions are satisfied:
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)Contents
[edit] Parameters
first
-
the beginning of the range of elements to destroy
n
-
the number of elements to destroy
policy
-
the execution policy to use
Type requirements
-
ForwardIt must meet the requirements of LegacyForwardIterator.
-No increment, assignment, comparison, or indirection through valid instances of
ForwardIt may throw exceptions.
[edit] Return value
The end of the range of objects that has been destroyed (i.e., std::next (first, n)).
[edit] Complexity
Linear in n.
[edit] 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.
[edit] 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; }
[edit] 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