std::add_pointer - cppreference.com (original) (raw)

| | | | | ----------------------------------------- | | ------------- | | template< class T > struct add_pointer; | | (since C++11) |

If T is a referenceable type or (possibly cv-qualified) void, the member typedef type provided is typename std::remove_reference<T>::type*.

Otherwise, the member typedef type provided is T.

If the program adds specializations for std::add_pointer, the behavior is undefined.

Contents

• 1 Nested types
• 2 Helper types
• 3 Possible implementation
• 4 Example
• 5 Defect reports
• 6 See also

[edit] Nested types

[edit] Helper types

| template< class T > using add_pointer_t = typename add_pointer<T>::type; | | (since C++14) | | ------------------------------------------------------------------------------ | | ------------- |

[edit] Possible implementation

namespace detail { template struct type_identity { using type = T; }; // or use std::type_identity (since C++20)   template auto try_add_pointer(int) -> type_identity<typename std::remove_reference::type*>; // usual case   template auto try_add_pointer(...) -> type_identity; // unusual case (cannot form std::remove_reference::type*) } // namespace detail   template struct add_pointer : decltype(detail::try_add_pointer(0)) {};

[edit] Example

#include #include   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; 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 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::type IntAgain; IntAgain j = i; std::cout << "j = " << j << '\n';   static_assert(, "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

[edit] Defect reports

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

[edit] See also