std::construct_at

Since C++20

Header: <memory>

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

# Declarations

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

(since C++20)

# Parameters

# Return value

location

# 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() {}

# Defect reports

DRApplied toBehavior as publishedCorrect behavior
LWG 3436C++20construct_at could not create objects of array typescan value-initialize bounded arrays
LWG 3870C++20construct_at could create objects of cv-qualified typesonly cv-unqualified types are permitted

# See also