std::to_address
From cppreference.com
Defined in header <memory>
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template< class Ptr > auto to_address(const Ptr& p) noexcept; |
(1) | (since C++20) |
template< class T > constexpr T* to_address(T* p) noexcept; |
(2) | (since C++20) |
Obtain the address represented by p
without forming a reference to the pointee.
1) Fancy pointer overload: If the expression std::pointer_traits<Ptr>::to_address(p) is well-formed, returns the result of that expression. Otherwise, returns std::to_address(p.operator->()).
2) Raw pointer overload: If
T
is a function type, the program is ill-formed. Otherwise, returns p unmodified.Parameters
p | - | fancy or raw pointer |
Return value
Raw pointer that represents the same address as p
does.
Possible implementation
template<class> struct use_address : std::false_type { }; template<class T> requires requires(const T& p) { std::pointer_traits<T>::to_address(p); } struct use_address<T> : std::true_type { }; template<class T> constexpr T* to_address(T* p) noexcept { static_assert(!std::is_function_v<T>); return p; } template<class T> auto to_address(const T& p) noexcept { if constexpr (use_address<T>::value) { return std::pointer_traits<T>::to_address(p); } else { return std::to_address(p.operator->()); } } |
Notes
std::to_address
can be used even when p
does not reference storage that has an object constructed in it, in which case std::addressof(*p) cannot be used because there's no valid object for the parameter of std::addressof to bind to.
Example
Run this code
#include <memory> template<class A> auto allocator_new(A& a) { auto p = a.allocate(1); try { std::allocator_traits<A>::construct(a, std::to_address(p)); } catch (...) { a.deallocate(p, 1); throw; } return p; } template<class A> void allocator_delete(A& a, typename std::allocator_traits<A>::pointer p) { std::allocator_traits<A>::destroy(a, std::to_address(p)); a.deallocate(p, 1); } int main() { std::allocator<int> a; auto p = allocator_new(a); allocator_delete(a, p); }
See also
(C++11) |
provides information about pointer-like types (class template) |
[static] (C++20) |
obtains a raw pointer from a fancy pointer (inverse of pointer_to) (public static member function of std::pointer_traits<Ptr> ) |