std::is_base_of

 

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is_copy_constructibleis_trivially_copy_constructibleis_nothrow_copy_constructible (C++11)(C++11)(C++11)
is_move_constructibleis_trivially_move_constructibleis_nothrow_move_constructible (C++11)(C++11)(C++11)
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is_move_assignableis_trivially_move_assignableis_nothrow_move_assignable (C++11)(C++11)(C++11)
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Defined in header <type_traits>
template< class Base, class Derived > struct is_base_of;		(since C++11)

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;		(since C++17)

Inherited from std::integral_constant

Member constants

value [static]

true if Derived is derived from Base , false otherwise (public static member constant)

Member functions

operator bool	converts the object to bool, returns value (public member function)
operator() (C++14)	returns value (public member function)

Member types

Type	Definition
value_type	bool
type	std::integral_constant<bool, 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

Run this code

#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';
}

Output:

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

See also

std::experimental::is_base_of_v (library fundamentals TS)

variable template alias of std::is_base_of::value (variable template)