< cpp‎ | memory
Utilities library
Language support
Type support (basic types, RTTI)
Library feature-test macros (C++20)
Dynamic memory management
Program utilities
Coroutine support (C++20)
Variadic functions
Debugging support
Three-way comparison
General utilities
Date and time
Function objects
Formatting library (C++20)
Relational operators (deprecated in C++20)
Integer comparison functions
Swap and type operations
Common vocabulary types
Elementary string conversions

Dynamic memory management
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Garbage collection support
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)

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

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 (static_cast<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.


[edit] Parameters

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

[edit] Return value


[edit] Example

#include <bit>
#include <memory>
class S
    int x_;
    float y_;
    double z_;
    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);
    S* ptr = std::construct_at(std::addressof(uninitialized), 42, 2.71f, 3.14);
    const bool res{*ptr == S{42, 2.71f, 3.14}};
    return res;
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 3870 C++20 construct_at could create objects of a 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