std::is_abstract

From Cppreference

Defined in header `<type_traits>`

template< class T > struct is_abstract;		(C++11 feature)

If T is an abstract class (that is, a 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.

Inherited from std::integral_constant

Member constants


`value`	true if `T` is an abstract class type , false otherwise (public static member constant)

Member functions


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

Member types


Type	Definition

`value_type`	`bool`

`type`	std::integral_constant<bool, value>

[edit] Notes

Abstract classes may only be used as base classes; no objects of an abstract class type can be created except in form of base class subobjects.

An abstract class may be derived from a class that is not abstract if a pure virtual function overrides a virtual function that is not pure.

[edit] Example

#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

[edit] See also

is_class (C++11)

checks if a type is a class type (but not union type)
(class template)

is_polymorphic (C++11)

checks if a type is polymorphic class type
(class template)