NAME¶

std::destroy_at - std::destroy_at

Synopsis¶

Defined in header <memory>
template< class T > (since C++17)
void destroy_at( T* p ); (until C++20)
template< class T > (since C++20)
constexpr void destroy_at( T* p );

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).

Parameters¶

p - a pointer to the object to be destroyed

Return value¶

(none)

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(); }

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 (since C++20)
began within the evaluation of e.

Example¶

The following example demonstrates how to use destroy_at to destroy a contiguous
sequence of elements.

// Run this code

#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

See also¶

destroy destroys a range of objects
(C++17) (function template)
destroy_n destroys a number of objects in a range
(C++17) (function template)
construct_at creates an object at a given address
(C++20) (function template)
ranges::destroy_at destroys an object at a given address
(C++20) (niebloid)