NAME

std::construct_at - std::construct_at

Synopsis

Defined in header <memory>
template<class T, class... Args> (since C++20)
constexpr T* construct_at( T* p, Args&&... args );

Creates a T object initialized with arguments args... at given address p.
Specialization of this function template participates in overload resolution only if
::new(std::declval<void*>()) T(std::declval<Args>()...) is well-formed in an
unevaluated context.

Equivalent to

return ::new (const_cast<void*>(static_cast<const volatile void*>(p)))
T(std::forward<Args>(args)...);

except that construct_at may be used in evaluation of constant expressions.

When construct_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.

Parameters

p - pointer to the uninitialized storage on which a T object will be
constructed
args... - arguments used for initialization

Return value

p

Example

// Run this code

#include <iostream>
#include <memory>

struct S {
int x;
float y;
double z;

S(int x, float y, double z) : x{x}, y{y}, z{z} { std::cout << "S::S();\n"; }

~S() { std::cout << "S::~S();\n"; }

void print() const {
std::cout << "S { x=" << x << "; y=" << y << "; z=" << z << "; };\n";
}
};

int main()
{
alignas(S) unsigned char storage[sizeof(S)];

S* ptr = std::construct_at(reinterpret_cast<S*>(storage), 42, 2.71828f, 3.1415);
ptr->print();

std::destroy_at(ptr);
}

Output:

S::S();
S { x=42; y=2.71828; z=3.1415; };
S::~S();

See also

allocate allocates uninitialized storage
(public member function of std::allocator<T>)
construct constructs an object in the allocated storage
[static] (function template)
destroy_at destroys an object at a given address
(C++17) (function template)
ranges::construct_at creates an object at a given address
(C++20) (niebloid)