std::is_abstract

 

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

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 [static]	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>

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.

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

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)