Difference between revisions of "cpp/memory/destroy n"
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{{dcl begin}} | {{dcl begin}} | ||
{{dcl header | memory}} | {{dcl header | memory}} | ||
| − | {{dcl | | + | {{dcl rev multi | num=1 |
| + | | since1=c++17 | dcl1= | ||
template< class ForwardIt, class Size > | template< class ForwardIt, class Size > | ||
ForwardIt destroy_n( ForwardIt first, Size n ); | ForwardIt destroy_n( ForwardIt first, Size n ); | ||
| + | | since2=c++20 | dcl2= | ||
| + | template< class ForwardIt, class Size > | ||
| + | constexpr ForwardIt destroy_n( ForwardIt first, Size n ); | ||
}} | }} | ||
| − | {{dcl | since=c++17 | | + | {{dcl | num=2 | since=c++17 | |
template< class ExecutionPolicy, class ForwardIt, class Size > | template< class ExecutionPolicy, class ForwardIt, class Size > | ||
| − | ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n );}} | + | ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n ); |
| + | }} | ||
{{dcl end}} | {{dcl end}} | ||
@1@ Destroys the {{tt|n}} objects in the range starting at {{tt|first}}, as if by | @1@ Destroys the {{tt|n}} objects in the range starting at {{tt|first}}, as if by | ||
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{{eq fun | 1= | {{eq fun | 1= | ||
template<class ForwardIt, class Size> | template<class ForwardIt, class Size> | ||
| + | constexpr // since C++20 | ||
ForwardIt destroy_n( ForwardIt first, Size n ) | ForwardIt destroy_n( ForwardIt first, Size n ) | ||
{ | { | ||
Revision as of 20:27, 6 February 2020
| Defined in header <memory>
|
||
| (1) | ||
template< class ForwardIt, class Size > ForwardIt destroy_n( ForwardIt first, Size n ); |
(since C++17) (until C++20) |
|
| 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 std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is trueContents |
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
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) |
