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std::destroy_n

From cppreference.com
< cpp‎ | memory
 
 
 
Dynamic memory management
Uninitialized storage
(C++17)
Garbage collection support
Miscellaneous
(C++20)
(C++11)
(C++11)
C Library
Low level memory management
 
Defined in header <memory>
template< class ForwardIt, class Size >
ForwardIt destroy_n( ForwardIt first, Size n );
(1) (since C++17)
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 std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

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. 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.

[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 ExecutionPolicy is one of the three 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.

[edit] Possible implementation

template<class ForwardIt, class Size>
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.

#include <memory>
#include <new>
#include <iostream>
 
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

[edit] See also

(C++17)
destroys a range of objects
(function template) [edit]
destroys an object at a given address
(function template) [edit]