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 (in both cases 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, and they are not the same type (ignoring cv-qualification), Derived
shall be a complete type; otherwise the behavior is undefined.
The behavior of a program that adds specializations for is_base_of
or is_base_of_v
(since C++17) is undefined.
template< class Base, class Derived > inline constexpr bool is_base_of_v = is_base_of<Base, Derived>::value; | (since C++17) |
value
[static] | true if Derived is derived from Base or if both are the same non-union class (in both cases ignoring cv-qualification), false otherwise (public static member constant) |
operator bool | converts the object to bool, returns value (public member function) |
operator()
(C++14) | returns value (public member function) |
Type | Definition |
---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
std::is_base_of<A, B>::value
is true
even if A
is a private, protected, or ambiguous base class of B
. In many situations, std::is_convertible<B*, A*>
is the more appropriate test.
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.
#include <type_traits> class A {}; class B : A {}; class C : B {}; class D {}; union E {}; static_assert(std::is_base_of_v<A, A> == true && std::is_base_of_v<A, B> == true && std::is_base_of_v<A, C> == true && std::is_base_of_v<A, D> == false && std::is_base_of_v<B, A> == false && std::is_base_of_v<E, E> == false && std::is_base_of_v<int, int> == false); int main() {}
(C++11)(C++20) | checks if a type can be converted to the other type (class template) |
(C++20) | specifies that a type is derived from another type (concept) |
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