| 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 (since C++17), 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 | (since C++17) |
| Name | Definition |
|---|---|
type | pointer to T or to the type referenced by T |
template< class T > using add_pointer_t = typename add_pointer<T>::type; | (since C++14) |
namespace detail {
template< class T, bool is_function_type = false >
struct add_pointer {
using type = typename std::remove_reference<T>::type*;
};
template< class T >
struct add_pointer<T, true> {
using type = T;
};
template< class T, class... Args >
struct add_pointer<T(Args...), true> {
using type = T(*)(Args...);
};
template< class T, class... Args >
struct add_pointer<T(Args..., ...), true> {
using type = T(*)(Args..., ...);
};
} // namespace detail
template< class T >
struct add_pointer : detail::add_pointer<T, std::is_function<T>::value> {}; |
#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
| (C++11)
| checks if a type is a pointer type (class template) |
| (C++11)
| removes pointer from the given type (class template) |
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