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 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.

The behavior of a program that adds specializations for add_pointer is undefined.

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>

template<typename F, typename Class>
void ptr_to_member_func_cvref_test(F Class::*)
{
// F is an "abominable function type"
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<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");

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 retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
std::add_pointer was required
LWG 2101 C++11 to produce Produces cv-/ref-qualified
pointer to cv-/ref-qualified function types themselves.
function types.

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)