std::is_abstract

 

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

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 > constexprbool is_abstract_v = is_abstract<T>::value;		(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

true if T is an abstract class 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>

Example

Run this code

#include <iostream>#include <type_traits>   struct A {int m;}; static_assert(std::is_abstract_v<A>==false);   struct B {virtualvoid foo();}; static_assert(std::is_abstract_v<B>==false);   struct C {virtualvoid foo()=0;}; static_assert(std::is_abstract_v<C>==true);   struct D : C {}; static_assert(std::is_abstract_v<D>==true);   struct E : C {void foo() override {}}; static_assert(std::is_abstract_v<E>==false);   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 T is an incomplete union type	the base characteristic is std::false_type in this case

See also

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