Difference between revisions of "cpp/memory/ranges/destroy at"
From cppreference.com
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Andreas Krug (Talk | contribs) m ({{c}}, fmt) |
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{{cpp/memory/navbar}} | {{cpp/memory/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | memory}} | + | {{dcl header|memory}} |
| − | {{dcl h | Call signature}} | + | {{dcl h|Call signature}} |
| − | {{dcl | since=c++20 | | + | {{dcl|since=c++20| |
template< std::destructible T > | template< std::destructible T > | ||
constexpr void destroy_at( T* p ) noexcept; | constexpr void destroy_at( T* p ) noexcept; | ||
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{{dcl end}} | {{dcl end}} | ||
| − | If {{tt|T}} is not an array type, calls the destructor of the object pointed to by {{ | + | If {{tt|T}} is not an array type, calls the destructor of the object pointed to by {{c|p}}, as if by {{tt|p->~T()}}. Otherwise, recursively destroys elements of {{c|*p}} in order, as if by calling {{c|std::destroy(std::begin(*p), std::end(*p))}}. |
{{cpp/ranges/niebloid}} | {{cpp/ranges/niebloid}} | ||
| Line 16: | Line 16: | ||
===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | p | a pointer to the object to be destroyed}} | + | {{par|p|a pointer to the object to be destroyed}} |
{{par end}} | {{par end}} | ||
| Line 23: | Line 23: | ||
===Possible implementation=== | ===Possible implementation=== | ||
| − | {{eq fun | 1= | + | {{eq fun|1= |
| − | struct destroy_at_fn { | + | struct destroy_at_fn |
| − | + | { | |
| − | + | template<std::destructible T> | |
| − | + | constexpr void operator()(T *p) const noexcept | |
| − | + | { | |
| − | + | if constexpr (std::is_array_v<T>) | |
| − | + | for (auto &elem : *p) | |
| − | + | operator()(std::addressof(elem)); | |
| − | + | else | |
| − | + | p->~T(); | |
| + | } | ||
}; | }; | ||
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{{tt|destroy_at}} deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call. | {{tt|destroy_at}} deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call. | ||
| − | When {{tt|destroy_at}} is called in the evaluation of some [[cpp/language/constant expression|constant expression]] {{c|e}}, the argument {{ | + | When {{tt|destroy_at}} is called in the evaluation of some [[cpp/language/constant expression|constant expression]] {{c|e}}, the argument {{c|p}} must point to an object whose lifetime began within the evaluation of {{c|e}}. |
===Example=== | ===Example=== | ||
| Line 49: | Line 50: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/memory/ranges/dsc destroy}} | + | {{dsc inc|cpp/memory/ranges/dsc destroy}} |
| − | {{dsc inc | cpp/memory/ranges/dsc destroy_n}} | + | {{dsc inc|cpp/memory/ranges/dsc destroy_n}} |
| − | {{dsc inc | cpp/memory/ranges/dsc construct_at}} | + | {{dsc inc|cpp/memory/ranges/dsc construct_at}} |
| − | {{dsc inc | cpp/memory/dsc destroy_at}} | + | {{dsc inc|cpp/memory/dsc destroy_at}} |
{{dsc end}} | {{dsc end}} | ||
{{langlinks|de|es|ja|ru|zh}} | {{langlinks|de|es|ja|ru|zh}} | ||
Latest revision as of 07:41, 15 June 2023
| Defined in header <memory>
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| Call signature |
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| template< std::destructible T > constexpr void destroy_at( T* p ) noexcept; |
(since C++20) | |
If T is not an array type, calls the destructor of the object pointed to by p, as if by p->~T(). Otherwise, recursively destroys elements of *p in order, as if by calling std::destroy(std::begin(*p), std::end(*p)).
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] Parameters
| p | - | a pointer to the object to be destroyed |
[edit] Return value
(none)
[edit] Possible implementation
struct destroy_at_fn { template<std::destructible T> constexpr void operator()(T *p) const noexcept { if constexpr (std::is_array_v<T>) for (auto &elem : *p) operator()(std::addressof(elem)); else p->~T(); } }; inline constexpr destroy_at_fn destroy_at{}; |
[edit] Notes
destroy_at deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call.
When destroy_at is called in the evaluation of some constant expression e, the argument p must point to an object whose lifetime began within the evaluation of e.
[edit] Example
The following example demonstrates how to use ranges::destroy_at 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)); for (int i = 0; i < 8; ++i) std::ranges::destroy_at(ptr + i); }
Output:
0 destructed 1 destructed 2 destructed 3 destructed 4 destructed 5 destructed 6 destructed 7 destructed
[edit] See also
| (C++20) |
destroys a range of objects (niebloid) |
| (C++20) |
destroys a number of objects in a range (niebloid) |
| (C++20) |
creates an object at a given address (niebloid) |
| (C++17) |
destroys an object at a given address (function template) |
