std::is_base_of

template< class Base, class Derived >
struct is_base_of;

If Derived is derived from Base or if both are the same non-union class, provides the member constant value equal to true. Otherwise value is false.

If both Base and Derived are non-union class types, and they are not the same type (ignoring cv-qualification), Derived shall be a complete type; otherwise the behavior is undefined.

Helper variable template

template< class Base, class Derived >
constexpr bool is_base_of_v = is_base_of<Base, Derived>::value;

Notes

Although no class is its own base, std::is_base_of<T, T>::value is true because the intent of the trait is to model the "is-a" relationship, and T is a T. Despite that, std::is_base_of<int, int>::value is false because only classes participate in the relationship that this trait models.

Example

#include <iostream>
#include <type_traits>
 
class A {};
 
class B : A {};
 
class C {};
 
int main() 
{
    std::cout << std::boolalpha;
    std::cout << "a2b: " << std::is_base_of<A, B>::value << '\n';
    std::cout << "b2a: " << std::is_base_of<B, A>::value << '\n';
    std::cout << "c2b: " << std::is_base_of<C, B>::value << '\n';
    std::cout << "same type: " << std::is_base_of<C, C>::value << '\n';
}

a2b: true
b2a: false
c2b: false
same type: true

See also