C++

Reference

<type_traits>

class template
<type_traits>

std::is_abstract

template <class T> struct is_abstract;
Is abstract class

Trait class that identifies whether T is an abstract class.

An abstract class is a class that has at least one pure virtual function.

is_abstract inherits from integral_constant as being either true_type or false_type, depending on whether T is a polymorphic class type.

Template parameters

T
A complete type, or void (possible cv-qualified), or an array of unknown bound of a complete element type.
A type.
If a class type, it shall be a complete type or a union (for unions, this trait is always false).

Member types

Inherited from integral_constant:
member typedefinition
value_typebool
typeeither true_type or false_type

Member constants

Inherited from integral_constant:
member constantdefinition
valueeither true or false

Member functions

Inherited from integral_constant:
operator bool
Returns value (public member function)

Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
 
// is_abstract example #include <iostream> #include <type_traits> struct A { }; struct B { virtual void fn() = 0; // pure virtual function }; struct C : B { }; struct D : C { virtual void fn(){} }; int main() { std::cout << std::boolalpha; std::cout << "is_abstract:" << std::endl; std::cout << "A: " << std::is_abstract<A>::value << std::endl; std::cout << "B: " << std::is_abstract<B>::value << std::endl; std::cout << "C: " << std::is_abstract<C>::value << std::endl; std::cout << "D: " << std::is_abstract<D>::value << std::endl; return 0; }

Output:
is_abstract: A: false B: true C: true D: false


See also

is_polymorphic
Is polymorphic (class template)
has_virtual_destructor
Has virtual destructor (class template)
is_trivial
Is trivial type (class template)