From cppreference.com
Defined in header
Call signature
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.
The function-like entities described on this page are
(informally known as niebloids), that is:
Explicit template argument lists cannot be specified when calling any of them.
None of them are visible to
.
When any of them are found by
as the name to the left of the function-call operator,
is inhibited.
Parameters
location - pointer to the uninitialized storage on which a T object will be constructed args... - arguments used for initialization Return value
location
Notes
std::ranges::construct_at behaves exactly same as
, except that it is invisible to argument-dependent lookup.
Example
Run this code
#include<iostream>#include<memory>structS{intx;floaty;doublez;S(intx,floaty,doublez):x{x},y{y},z{z}{std::cout<<"S::S();\n";}~S(){std::cout<<"S::~S();\n";}voidprint()const{std::cout<<"S { x="<<x<<"; y="<<y<<"; z="<<z<<"; };\n";}};intmain(){alignas(S)unsignedcharbuf[sizeof(S)];S*ptr=std::ranges::construct_at(reinterpret_cast<S*>(buf),42,2.71828f,3.1415);ptr->print();std::ranges::destroy_at(ptr);}Output:
S::S(); S { x=42; y=2.71828; z=3.1415; }; S::~S(); 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