# std::add_pointer

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< cpp‎ | types

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 `std::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

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_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

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)

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