Difference between revisions of "cpp/memory/construct at"
From cppreference.com
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| − | Creates a {{tt|T}} object initialized with arguments {{tt|args...}} at given address {{tt|p}}. | + | Creates a {{tt|T}} object initialized with arguments {{tt|args...}} at given address {{tt|p}}. Specialization of this function template participates in overload resolution only if {{c|::new(std::declval<void*>()) T(std::declval<Args>()...)}} is well-formed in unevaluated context. |
Equivalent to | Equivalent to | ||
Revision as of 22:51, 31 August 2020
| Defined in header <memory>
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| 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 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.
Contents |
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
| allocates uninitialized storage (public member function of std::allocator<T>)
| |
| [static] |
constructs an object in the allocated storage (function template) |
| (C++17) |
destroys an object at a given address (function template) |
