std::add_pointer

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

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 >
using add_pointer_t = typename add_pointer<T>::type;

(since C++14)

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

#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 pointer to cv-/ref-qualified function types.	Produces cv-/ref-qualified function types themselves.

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