std::add_pointer
From cppreference.com
Defined in header <type_traits>
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||
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
Run this code
#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 producepointer 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) |