std:: is_virtual_base_of

std::is_virtual_base_of is a BinaryTypeTrait .

If Base is a virtual base class of Derived (ignoring cv-qualification), provides the member constant value equal to true . Otherwise value is false .

If both Base and Derived are non-union class types (ignoring cv-qualification), Derived should be a complete type ; otherwise the behavior is undefined.

If the program adds specializations for std::is_virtual_base_of or std::is_virtual_base_of_v , the behavior is undefined.

Helper variable template

Notes

std :: is_virtual_base_of_v < A, B > is true even if A is a private, protected, or ambiguous base class of B .

If std :: is_virtual_base_of_v < A, B > is true , then std:: is_base_of_v < A, B > is also true . However, the converse is not always true because the check for virtual inheritance is more specific. In that case, std :: is_virtual_base_of_v < T, T > is false even if T is a non-union class type.

Example

#include <type_traits>
 
class A {};
class B : A {};
class C : B {};
class D : virtual A {};
class E : D {};
 
union F {};
using I = int;
 
static_assert
(
    std::is_virtual_base_of_v<A, A> != true &&
    std::is_virtual_base_of_v<A, B> != true &&
    std::is_virtual_base_of_v<A, D> == true &&
    std::is_virtual_base_of_v<D, E> != true &&
    std::is_virtual_base_of_v<F, F> != true &&
    std::is_virtual_base_of_v<I, I> != true
);
 
int main() {}

See also