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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.

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 >
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>
 
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_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 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.

See also

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

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