template< class Base, class Derived >
struct 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.
template< class Base, class Derived >
constexpr bool is_virtual_base_of_v = is_virtual_base_of<Base, Derived>::value;
Derived is derived from virtual base class Base (ignoring cv-qualification), false otherwise
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.
#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() {}[edit] See also
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