std::is_base_of
From cppreference.com
| 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.
Contents |
[edit] 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> |
[edit] 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.
[edit] 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
[edit] See also
| (library fundamentals TS) |
variable template alias of std::is_base_of::value (variable template) |