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std::is_abstract(3) C++ Standard Libary std::is_abstract(3) NAME std::is_abstract - std::is_abstract Synopsis Defined in header <type_traits> template< class T > (since C++11) struct is_abstract; std::is_abstract is a UnaryTypeTrait. If T is an abstract class (that is, a non-union class that declares or inherits at least one pure virtual function), provides the member constant value equal to true. For any other type, value is false. If T is an incomplete non-union class type, the behavior is unde- fined. If the program adds specializations for std::is_abstract or std::is_abstract_v, the behavior is undefined. Template parameters T - a type to check Helper variable template template< class T > (since C++17) inline constexpr bool is_abstract_v = is_abstract<T>::value; Inherited from std::integral_constant Member constants value true if T is an abstract class type, false otherwise [static] (public static member constant) Member functions operator bool converts the object to bool, returns value (public member function) operator() returns value (C++14) (public member function) Member types Type Definition value_type bool type std::integral_constant<bool, value> Example // Run this code #include <iostream> #include <type_traits> struct A { int m; }; static_assert(std::is_abstract_v<A> == false); struct B { virtual void foo(); }; static_assert(std::is_abstract_v<B> == false); struct C { virtual void foo() = 0; }; static_assert(std::is_abstract_v<C> == true); struct D : C {}; static_assert(std::is_abstract_v<D> == true); int main() {} Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct be- havior LWG 2015 C++11 the behavior was undefined if the base charac- teristic is T is an incomplete union type std::false_type in this case See also is_class checks if a type is a non-union class type (C++11) (class template) is_polymorphic checks if a type is a polymorphic class type (C++11) (class template) http://cppreference.com 2024.06.10 std::is_abstract(3)
NAME | Synopsis | Template parameters | Member constants | Member functions | Member types | Example | See also
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