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std::add_pointer(3)	       C++ Standard Libary	     std::add_pointer(3)

NAME
     std::add_pointer - std::add_pointer

Synopsis
	Defined in header <type_traits>
	template< class T >		 (since C++11)
	struct add_pointer;

	If T is a referenceable type or (possibly cv-qualified) void, the member
     typedef
	type provided is typename std::remove_reference::type<T>*.

	Otherwise, the member typedef type provided is T.

	If  the  program adds specializations for std::add_pointer, the behavior
     is undefined.

Helper types
	template< class T >				      (since C++14)
	using add_pointer_t = typename add_pointer<T>::type;

Possible implementation
       namespace detail
       {
	   template<class T>
	   struct type_identity { using type = T; }; // or  use  std::type_iden-
     tity (since C++20)

	   template<class T>
	   auto try_add_pointer(int)
	     ->   type_identity<typename   std::remove_reference<T>::type*>;  //
     usual case

	   template<class T>
	   auto try_add_pointer(...)
	     -> type_identity<T>; // unusual case (cannot form	std::remove_ref-
     erence<T>::type*)
       } // namespace detail

       template<class T>
       struct add_pointer : decltype(detail::try_add_pointer<T>(0)) {};

Example
     // Run this code

      #include <iostream>
      #include <type_traits>

      template<typename F, typename Class>
      void ptr_to_member_func_cvref_test(F Class::*)
      {
	  // F is an aabominable function typea
	  using FF = std::add_pointer_t<F>;
	  static_assert(std::is_same_v<F, FF>, "FF should be precisely F");
      }

      struct S
      {
	  void f_ref() & {}
	  void f_const() const {}
      };

      int main()
      {
	  int i = 123;
	  int& ri = i;
	  typedef std::add_pointer<decltype(i)>::type IntPtr;
	  typedef std::add_pointer<decltype(ri)>::type IntPtr2;
	  IntPtr pi = &i;
	  std::cout << "i = " << i << '\n';
	  std::cout << "*pi = " << *pi << '\n';

	  static_assert(std::is_pointer_v<IntPtr>,    "IntPtr	 should   be   a
     pointer");
	  static_assert(std::is_same_v<IntPtr,	int*>,	"IntPtr  should   be   a
     pointer to int");
	  static_assert(std::is_same_v<IntPtr2,   IntPtr>,  "IntPtr2  should  be
     equal to IntPtr");

	  typedef std::remove_pointer<IntPtr>::type IntAgain;
	  IntAgain j = i;
	  std::cout << "j = " << j << '\n';

	  static_assert(!std::is_pointer_v<IntAgain>, "IntAgain should not be  a
     pointer");
	  static_assert(std::is_same_v<IntAgain, int>, "IntAgain should be equal
     to int");

	  ptr_to_member_func_cvref_test(&S::f_ref);
	  ptr_to_member_func_cvref_test(&S::f_const);
      }

Output:
      i = 123
      *pi = 123
      j = 123

	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	    Behavior as  published		 Correct
     behavior
	LWG 2101 C++11	    the program was ill-formed if T is a   the type pro-
     duced is T in
			    function type with cv or ref	   this case

See also
	is_pointer     checks if a type is a pointer type
	(C++11)        (class template)
	remove_pointer removes a pointer from the given type
	(C++11)        (class template)

http://cppreference.com 	   2024.06.10		     std::add_pointer(3)
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