std::ranges::construct_at - cppreference.com (original) (raw)

| Defined in header | | | | ------------------------------------------------------------------------------------------------ | | ------------- | | Call signature | | | | 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_](../voidify.html "cpp/memory/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.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

[edit] Parameters

[edit] Return value

location

[edit] Notes

std::ranges::construct_at behaves exactly same as std::construct_at, except that it is invisible to argument-dependent lookup.

[edit] Example

#include #include   struct S { int x; float y; double z;   S(int x, float y, double z) : x{x}, y{y}, z{z} { std::cout << "S::S();\n"; }   S() { std::cout << "S::S();\n"; }   void print() const { std::cout << "S { x=" << x << "; y=" << y << "; z=" << z << "; };\n"; } };   int main() { alignas(S) unsigned char buf[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();

[edit] Defect reports

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

[edit] See also