NAME¶

std::is_abstract - std::is_abstract

Synopsis¶

Defined in header <type_traits>
template< class T > (since C++11)
struct is_abstract;

std::is_abstract is a UnaryTypeTrait.

If T is an abstract class (that is, a non-union class that declares or inherits at
least one pure virtual function), provides the member constant value equal to true.
For any other type, value is false.

If T is an incomplete non-union class type, the behavior is undefined.

If the program adds specializations for std::is_abstract or std::is_abstract_v, the
behavior is undefined.

Template parameters¶

T - a type to check

Helper variable template

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

Inherited from std::integral_constant

Member constants¶

value true if T is an abstract class type, false otherwise
[static] (public static member constant)

Member functions¶

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

Member types¶

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

Example¶

// Run this code

#include <iostream>
#include <type_traits>

struct A { int m; };
static_assert(std::is_abstract_v<A> == false);

struct B { virtual void foo(); };
static_assert(std::is_abstract_v<B> == false);

struct C { virtual void foo() = 0; };
static_assert(std::is_abstract_v<C> == true);

struct D : C {};
static_assert(std::is_abstract_v<D> == true);

int main() {}

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 2015 C++11 the behavior was undefined if the base characteristic is
T is an incomplete union type std::false_type in this case

See also¶

is_class checks if a type is a non-union class type
(C++11) (class template)
is_polymorphic checks if a type is a polymorphic class type
(C++11) (class template)