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Showing content from https://en.cppreference.com/w/cpp/language/../memory/construct_at.html below:

std::construct_at - cppreference.com

template< class T, class... Args > constexpr T* construct_at( T* location, Args&&... args );

(since C++20)

Creates a T object initialized with the arguments in args at given address location.

Equivalent to if constexpr (std::is_array_v<T>) return ::new (voidify (*location)) T[1](); else return ::new (voidify (*location)) T(std::forward<Args>(args)...);, except that construct_at may be used in evaluation of constant expressions(until C++26).

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

This overload participates in overload resolution only if all following conditions are satisfied:

std::is_unbounded_array_v<T> is false.
::new(std::declval<void*>()) T(std::declval<Args>()...) is well-formed when treated as an unevaluated operand.

If std::is_array_v<T> is true and sizeof...(Args) is nonzero, the program is ill-formed.

[edit] Parameters location - pointer to the uninitialized storage on which a T object will be constructed args... - arguments used for initialization [edit] Return value

location

[edit] Example

#include <bit>
#include <memory>
 
class S
{
    int x_;
    float y_;
    double z_;
public:
    constexpr S(int x, float y, double z) : x_{x}, y_{y}, z_{z} {}
    [[nodiscard("no side-effects!")]]
    constexpr bool operator==(const S&) const noexcept = default;
};
 
consteval bool test()
{
    alignas(S) unsigned char storage[sizeof(S)]{};
    S uninitialized = std::bit_cast<S>(storage);
    std::destroy_at(&uninitialized);
    S* ptr = std::construct_at(std::addressof(uninitialized), 42, 2.71f, 3.14);
    const bool res{*ptr == S{42, 2.71f, 3.14}};
    std::destroy_at(ptr);
    return res;
}
static_assert(test());
 
int main() {}

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior LWG 3436 C++20 construct_at could not create objects of array types can value-initialize bounded arrays LWG 3870 C++20 construct_at could create objects of cv-qualified types only cv-unqualified types are permitted [edit] See also allocates uninitialized storage
(public member function of std::allocator<T>) [edit] constructs an object in the allocated storage
(function template) [edit] destroys an object at a given address
(function template) [edit] creates an object at a given address
(algorithm function object)[edit]

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