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std::is_pointer

From cppreference.com
< cpp‎ | types
 
 
Metaprogramming library
Type traits
Type categories
(C++11)
(C++14)  
(C++11)
is_pointer
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
Type properties
(C++11)
(C++11)
(C++14)
(C++11)
(C++11)(until C++20)
(C++11)(deprecated in C++20)
(C++11)
Type trait constants
Metafunctions
(C++17)
Supported operations
Relationships and property queries
Type modifications
(C++11)(C++11)(C++11)
Type transformations
(C++11)(deprecated in C++23)
(C++11)(deprecated in C++23)
(C++11)
(C++11)
(C++17)

(C++11)(until C++20)(C++17)
Compile-time rational arithmetic
Compile-time integer sequences
 
Defined in header <type_traits>
template< class T >
struct is_pointer;
(since C++11)

Checks whether T is a pointer to object or a pointer to function (but not a pointer to member/member function) or a cv-qualified version thereof. Provides the member constant value which is equal to true, if T is a object/function pointer type. Otherwise, value is equal to false.

The behavior of a program that adds specializations for is_pointer or is_pointer_v (since C++17) is undefined.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

template< class T >
inline constexpr bool is_pointer_v = is_pointer<T>::value;
(since C++17)

Inherited from std::integral_constant

Member constants

value
[static]
true if T is a pointer type , false otherwise
(public static member constant)

Member functions

operator bool
converts the object to bool, returns value
(public member function)
operator()
(C++14)
returns value
(public member function)

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>

[edit] Possible implementation

template<class T>
struct is_pointer : std::false_type {};
 
template<class T>
struct is_pointer<T*> : std::true_type {};
 
template<class T>
struct is_pointer<T* const> : std::true_type {};
 
template<class T>
struct is_pointer<T* volatile> : std::true_type {};
 
template<class T>
struct is_pointer<T* const volatile> : std::true_type {};

[edit] Example

#include <type_traits>
 
int main()
{
    class A {};
 
    static_assert(
           not std::is_pointer<A>::value
        && not std::is_pointer_v<A>   // same thing as above, but in C++17!
        && not std::is_pointer<A>()   // same as above, using inherited operator bool
        && not std::is_pointer<A>{}   // ditto
        && not std::is_pointer<A>()() // same as above, using inherited operator()
        && not std::is_pointer<A>{}() // ditto
        &&     std::is_pointer<A *>::value
        &&     std::is_pointer<A const * volatile>()
        && not std::is_pointer<A &>::value
        && not std::is_pointer<int>::value
        &&     std::is_pointer<int *>::value
        &&     std::is_pointer<int **>::value
        && not std::is_pointer<int[10]>::value
        && not std::is_pointer<std::nullptr_t>::value
    );
}

[edit] See also

checks if a type is a pointer to an non-static member function or object
(class template) [edit]
checks if a type is a pointer to a non-static member object
(class template) [edit]
checks if a type is a pointer to a non-static member function
(class template) [edit]
(C++11)
checks if a type is an array type
(class template) [edit]
(C++11)
checks if a type is a scalar type
(class template) [edit]