23 General utilities library [utilities]

23.10 Memory [memory]

23.10.3 Pointer traits [pointer.traits]

The class template pointer_­traits supplies a uniform interface to certain attributes of pointer-like types.
namespace std {
  template<class Ptr> struct pointer_traits {
    using pointer         = Ptr;
    using element_type    = see below;
    using difference_type = see below;

    template<class U> using rebind = see below;

    static pointer pointer_to(see below r);
  };

  template<class T> struct pointer_traits<T*> {
    using pointer         = T*;
    using element_type    = T;
    using difference_type = ptrdiff_t;

    template<class U> using rebind = U*;

    static pointer pointer_to(see below r) noexcept;
  };
}

23.10.3.1 Pointer traits member types [pointer.traits.types]

using element_type = see below;
Type: Ptr​::​element_­type if the qualified-id Ptr​::​element_­type is valid and denotes a type ([temp.deduct]); otherwise, T if Ptr is a class template instantiation of the form SomePointer<T, Args>, where Args is zero or more type arguments; otherwise, the specialization is ill-formed.
using difference_type = see below;
Type: Ptr​::​difference_­type if the qualified-id Ptr​::​difference_­type is valid and denotes a type ([temp.deduct]); otherwise, ptrdiff_­t.
template<class U> using rebind = see below;
Alias template: Ptr​::​rebind<U> if the qualified-id Ptr​::​rebind<U> is valid and denotes a type ([temp.deduct]); otherwise, SomePointer<U, Args> if Ptr is a class template instantiation of the form SomePointer<T, Args>, where Args is zero or more type arguments; otherwise, the instantiation of rebind is ill-formed.

23.10.3.2 Pointer traits member functions [pointer.traits.functions]

static pointer pointer_traits::pointer_to(see below r); static pointer pointer_traits<T*>::pointer_to(see below r) noexcept;
Remarks: If element_­type is cv void, the type of r is unspecified; otherwise, it is element_­type&.
Returns: The first member function returns a pointer to r obtained by calling Ptr​::​pointer_­to(r) through which indirection is valid; an instantiation of this function is ill-formed if Ptr does not have a matching pointer_­to static member function.
The second member function returns addressof(r).

23.10.3.3 Pointer traits optional members [pointer.traits.optmem]

Specializations of pointer_­traits may define the member declared in this subclause to customize the behavior of the standard library.
static element_type* to_address(pointer p) noexcept;
Returns: A pointer of type element_­type* that references the same location as the argument p.
[Note
:
This function should be the inverse of pointer_­to.
If defined, it customizes the behavior of the non-member function to_­address ([pointer.conversion]).
end note
]