20 General utilities library [utilities]

20.10 Memory [memory]

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

20.10.3.1 Member types [pointer.traits.types]

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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.

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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.

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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.

20.10.3.2 Member functions [pointer.traits.functions]

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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&.

20.10.3.3 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.

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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

]