table of contents
std::construct_at(3) | C++ Standard Libary | std::construct_at(3) |
NAME¶
std::construct_at - std::construct_at
Synopsis¶
Defined in header <memory>
template<class T, class... Args> (since C++20)
constexpr T* construct_at( T* p, Args&&... args );
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 (const_cast<void*>(static_cast<const volatile
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.
Parameters¶
p - pointer to the uninitialized storage on which a T object will
be
constructed
args... - arguments used for initialization
Return value¶
p
Example¶
// Run this code
#include <iostream>
#include <memory>
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 storage[sizeof(S)];
S* ptr = std::construct_at(reinterpret_cast<S*>(storage), 42, 2.71828f,
3.1415);
ptr->print();
std::destroy_at(ptr);
}
Output:¶
S::S();
S { x=42; y=2.71828; z=3.1415; };
S::~S();
See also¶
allocate allocates uninitialized storage
(public member function of std::allocator<T>)
construct constructs an object in the allocated storage
[static] (function template)
destroy_at destroys an object at a given address
(C++17) (function template)
ranges::construct_at creates an object at a given address
(C++20) (niebloid)
2022.07.31 | http://cppreference.com |