Std::add_pointer (3) Linux Manual Page

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 reference type, then provides the member typedef type which is a pointer to the referred type.
Otherwise, if T names an object type, a function type that is not cv- or ref-qualified, or a (possibly cv-qualified) void type, provides the member typedef type which is the type T*.
Otherwise (if T is a cv- or ref-qualified function type), provides the member typedef type which is the type T.

Member types

Name Definition
type pointer to T or to the type referenced by T

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_identity (since C++20)

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

} // namespace detail

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

Example

// Run this code

#include <iostream>

#include <type_traits>
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<IntPtr>::value, "IntPtr should be a pointer");
    static_assert(std::is_same<IntPtr, int *>::value, "IntPtr should be a pointer to int");
    static_assert(std::is_same<IntPtr2, IntPtr>::value, "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<IntAgain>::value, "IntAgain should not be a pointer");
    static_assert(std::is_same<IntAgain, int>::value, "IntAgain should be equal to int");
}

Output:

  i = 123
  *pi = 123
  j = 123

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG_2101 C++11 std::add_pointer was required to produce Produces cv-/ref-qualified function types themselves.
pointer to cv-/ref-qualified function types.

std::add_pointer (3) Linux Manual Page