From cppreference.com
template<classT,class...Args>constexprT*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
ifconstexpr(std::is_array_v<T>)
return::new(
(*location))T[1]();
else
return::new(
(*location))T(std::forward<Args>(args)...);, except that construct_at may be used in evaluation of
(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
.
If std::is_array_v<T> is true and sizeof...(Args) is nonzero, the program is ill-formed.
Parameters
location - pointer to the uninitialized storage on which a T object will be constructed args... - arguments used for initialization Return value
location
Example
Run this code
#include<bit>#include<memory>classS{intx_;floaty_;doublez_;public:constexprS(intx,floaty,doublez):x_{x},y_{y},z_{z}{}constexprbooloperator==(constS&)constnoexcept=default;};constevalbooltest(){std::allocator<S>allocator;S*uninitialized=allocator.allocate(1);S*ptr=std::construct_at(uninitialized,42,2.71f,3.14);constboolres{*ptr==S{42,2.71f,3.14}};std::destroy_at(ptr);allocator.deallocate(uninitialized,1);returnres;}static_assert(test());intmain(){}Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++20 construct_at could not create objects of array types can value-initialize bounded arrays See also