std::is_abstract (3) - Linux Manuals

std::is_abstract: std::is_abstract

NAME

std::is_abstract - std::is_abstract

Synopsis

Defined in header <type_traits>
template< class T > (since C++11)
struct is_abstract;

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 true. For any other type, value is false.
If T is a non-union class type, T shall be a complete type; otherwise, 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
         (public static member constant)
[static]

Member functions

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

operator() returns value
              (public member function)
(C++14)

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;
  };

  struct B {
      virtual void foo();
  };

  struct C {
      virtual void foo() = 0;
  };

  struct D : C {};

  int main()
  {
      std::cout << std::boolalpha;
      std::cout << std::is_abstract<A>::value << '\n';
      std::cout << std::is_abstract<B>::value << '\n';
      std::cout << std::is_abstract<C>::value << '\n';
      std::cout << std::is_abstract<D>::value << '\n';
  }

Output:

  false
  false
  true
  true