std::is_abstract

template< class T >
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.

The behavior of a program that adds specializations for std::is_abstract or std::is_abstract_v is undefined.

Template parameters

Helper variable template

template< class T >
inline constexpr bool is_abstract_v = is_abstract<T>::value;

Example

#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.

See also