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

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The definitions in this subclause make use of the following exposition-only class template and concept: template<class T> struct ptr-traits-elem / exposition only { }; template<class T> requires { typename T::element_type; } struct ptr-traits-elem<T> { using type = T::element_type; }; template<template<class.> class SomePointer, class T, class. Args> requires (!requires { typename SomePointer<T, Args..>::element_type; }) struct ptr-traits-elem<SomePointer<T, Args..> { using type = T; }; template<class Ptr> concept has-elem-type = / exposition only requires { typename ptr-traits-elem<Ptr>::type; }
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If Ptr satisfies has-elem-type, a specialization pointer_traits<Ptr> generated from the pointer_traits primary template has the following members as well as those described in [pointer.traits.functions]; otherwise, such a specialization has no members by any of those names.
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using pointer = see below;
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Type: Ptr.
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using element_type = see below;
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Type: typename ptr-traits-elem<Ptr>​::​type.
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using difference_type = see below;
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Type: Ptr​::​difference_type if the qualified-id Ptr​::​difference_type is valid and denotes a type ([temp.deduct]); otherwise, ptrdiff_t.
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template<class U> using rebind = see below;
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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.
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static constexpr pointer pointer_traits::pointer_to(see below r); static constexpr pointer pointer_traits<T*>::pointer_to(see below r) noexcept;
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Mandates: For the first member function, Ptr​::​pointer_to(r) is well-formed.
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Preconditions: For the first member function, Ptr​::​pointer_to(r) returns a pointer to r through which indirection is valid.
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Remarks: If element_type is cv void, the type of r is unspecified; otherwise, it is element_type&.
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Specializations of pointer_traits may define the member declared in this subclause to customize the behavior of the standard library.
A specialization generated from the pointer_traits primary template has no member by this name.
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static element_type* to_address(pointer p) noexcept;
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Returns: A pointer of type element_type* that references the same location as the argument p.
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[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]

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