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std::to_address

From cppreference.com
< cpp‎ | memory
 
 
 
Dynamic memory management
Uninitialized storage
(C++17)
Garbage collection support
Miscellaneous
to_address
(C++20)
(C++11)
(C++11)
C Library
Low level memory management
 
Defined in header <memory>
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.

Contents

[edit] Parameters

p - fancy or raw pointer

[edit] Return value

Raw pointer that represents the same address as p does.

[edit] Possible implementation

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 (requires{ std::pointer_traits<T>::to_address(p); }) {
        return std::pointer_traits<T>::to_address(p);
    } else {
        return std::to_address(p.operator->());
    }
}

[edit] 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.

[edit] Example

#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);
}


[edit] See also

provides information about pointer-like types
(class template) [edit]
[static] (C++20)
obtains a raw pointer from a fancy pointer (inverse of pointer_to)
(public static member function of std::pointer_traits<Ptr>) [edit]