20 Memory management library [mem]

20.2 Memory [memory]

20.2.3 Pointer traits [pointer.traits]

20.2.3.1 General [pointer.traits.general]

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

20.2.3.2 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.

20.2.3.3 Member functions [pointer.traits.functions]

static pointer pointer_traits::pointer_to(see below r); static constexpr pointer pointer_traits<T*>::pointer_to(see below r) noexcept;
Mandates: For the first member function, Ptr​::​pointer_­to(r) is well-formed.
Preconditions: For the first member function, Ptr​::​pointer_­to(r) returns a pointer to r through which indirection is valid.
Returns: The first member function returns Ptr​::​pointer_­to(r).
The second member function returns addressof(r).
Remarks: If element_­type is cv void, the type of r is unspecified; otherwise, it is element_­type&.

20.2.3.4 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 1:
This function is intended to be the inverse of pointer_­to.
If defined, it customizes the behavior of the non-member function to_­address ([pointer.conversion]).
— end note]