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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)

std::is_pointer is a UnaryTypeTrait.

Checks whether T is a pointer to object or function (including pointer to void, but excluding pointer to member) or a cv-qualified version thereof. Provides the member constant value which is equal to true, if T is an object/function pointer type. Otherwise, value is equal to false.

If the program adds specializations for std::is_pointer or std::is_pointer_v, the behavior is undefined.

Contents

[edit] Template parameters

T - a type to check

[edit] Helper variable template

template< class T >
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()
{
    struct A
    {
        int m;
        void f() {}
    };
 
    int A::*mem_data_ptr = &A::m;     // a pointer to member data
    void (A::*mem_fun_ptr)() = &A::f; // a pointer to member function
 
    static_assert(
           ! std::is_pointer<A>::value
        && ! std::is_pointer_v<A>    // same thing as above, but in C++17!
        && ! std::is_pointer<A>()    // same as above, using inherited operator bool
        && ! std::is_pointer<A>{}    // ditto
        && ! std::is_pointer<A>()()  // same as above, using inherited operator()
        && ! std::is_pointer<A>{}()  // ditto
        &&   std::is_pointer_v<A*>
        &&   std::is_pointer_v<A const* volatile>
        && ! std::is_pointer_v<A&>
        && ! std::is_pointer_v<decltype(mem_data_ptr)>
        && ! std::is_pointer_v<decltype(mem_fun_ptr)>
        &&   std::is_pointer_v<void*>
        && ! std::is_pointer_v<int>
        &&   std::is_pointer_v<int*>
        &&   std::is_pointer_v<int**>
        && ! std::is_pointer_v<int[10]>
        && ! std::is_pointer_v<std::nullptr_t>
        &&   std::is_pointer_v<void (*)()>
    );
}

[edit] See also

checks if a type is a pointer to a 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]