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std::is_abstract

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Revision as of 15:50, 1 July 2013 by P12bot (Talk | contribs)

 
 
 
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is_abstract
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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.

Contents

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

Member types

Type Definition
value_type bool
type std::integral_constant<bool, value>
[edit template]

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

(C++11)
checks if a type is a class type (but not union type)
(class template) [edit]
checks if a type is polymorphic class type
(class template) [edit]