std::is_virtual_base_of - cppreference.com (original) (raw)
| | | | | -------------------------------------------------------------------- | | ------------- | | template< class Base, class Derived > struct is_virtual_base_of; | | (since C++26) |
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.
Contents
[edit] Helper variable template
| template< class Base, class Derived > constexpr bool is_virtual_base_of_v = is_virtual_base_of<Base, Derived>::value; | | (since C++26) | | ------------------------------------------------------------------------------------------------------------------------------- | | ------------- |
Inherited from std::integral_constant
Member constants
| | true if Derived is derived from virtual base class Base (ignoring cv-qualification), false otherwise (public static member constant) | | --------------------------------------------------------------------------------------------------------------------------------------- |
Member functions
| | converts the object to bool, returns value (public member function) | | ---------------------------------------------------------------------- | | | returns value (public member function) |
Member types
[edit] 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.
[edit] Example
#include 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() {}