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std::destroy_at

From cppreference.com
< cpp‎ | memory
 
 
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Defined in header <memory>
template< class T >
void destroy_at( T* p );
(since C++17)
(until C++20)
template< class T >
constexpr void destroy_at( T* p );
(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().

If T is an array type, the program is ill-formed (until C++20)recursively destroys elements of *p in order, as if by calling std::destroy(std::begin(*p), std::end(*p)) (since C++20).

When destroy_at is called in the evaluation of some constant expression e, the argument p must point to either storage obtained by std::allocator<T>::allocate or an object whose lifetime began within the evaluation of e.

(since C++20)

Contents

[edit] Parameters

p - a pointer to the object to be destroyed

[edit] Return value

(none)

[edit] Possible implementation

template<class T>
constexpr void destroy_at(T* p) 
{
    if constexpr (std::is_array_v<T>)
        for (auto &elem : *p)
            destroy_at(std::addressof(elem));
    else
        p->~T(); 
}
// C++17 version:
// template<class T> void destroy_at(T* p) { p->~T(); }

[edit] Notes

destroy_at deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call.

[edit] Example

The following example demonstrates how to use destroy_at 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));
 
    for (int i = 0; i < 8; ++i)
        std::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++17)
destroys a range of objects
(function template) [edit]
(C++17)
destroys a number of objects in a range
(function template) [edit]
creates an object at a given address
(function template) [edit]