std::is_abstract – cppreference.com

std::is_abstract

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C++
 
Utilities-Bibliothek
 
Geben Sie Unterstützung
Grundtypen
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Basic types
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Grundtypen
Feste Breite Integer-Typen (C++11)
Numerische Grenzen
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Numeric limits
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numeric_limits
C numerische begrenzt Schnittstelle
Laufzeit-Typinformationen
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Runtime type information
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Exterieur
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Type traits
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Primären Typ Kategorien
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Primary type categories
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is_void(C++11)
is_array(C++11)
is_pointer(C++11)
is_enum(C++11)
is_union(C++11)
is_class(C++11)
is_function(C++11)
is_object(C++11)
is_scalar(C++11)
is_compound(C++11)
is_integral(C++11)
is_floating_point(C++11)
is_fundamental(C++11)
is_arithmetic(C++11)
is_reference(C++11)
is_lvalue_reference(C++11)
is_rvalue_reference(C++11)
is_member_pointer(C++11)
is_member_object_pointer(C++11)
is_member_function_pointer(C++11)
Typ Eigenschaften
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Type properties
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is_const(C++11)
is_volatile(C++11)
is_pod(C++11)
is_empty(C++11)
is_polymorphic(C++11)
is_abstract(C++11)
Unterstützte Operationen
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Supported operations
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is_constructible
is_trivially_constructible
is_nothrow_constructible		(C++11)
(C++11)
(C++11)
is_default_constructible
is_trivially_default_constructible
is_nothrow_default_constructible		(C++11)
(C++11)
(C++11)
is_copy_constructible
is_trivially_copy_constructible
is_nothrow_copy_constructible		(C++11)
(C++11)
(C++11)
is_move_constructible
is_trivially_move_constructible
is_nothrow_move_constructible		(C++11)
(C++11)
(C++11)
is_assignable
is_trivially_assignable
is_nothrow_assignable		(C++11)
(C++11)
(C++11)
is_copy_assignable
is_trivially_copy_assignable
is_nothrow_copy_assignable		(C++11)
(C++11)
(C++11)
is_move_assignable
is_trivially_move_assignable
is_nothrow_move_assignable		(C++11)
(C++11)
(C++11)
is_destructible
is_trivially_destructible
is_nothrow_destructible		(C++11)
(C++11)
(C++11)
has_virtual_destructor(C++11)
Beziehungen und Eigentum Abfragen
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Relationships and property queries
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is_same(C++11)
is_base_of(C++11)
is_convertible(C++11)
alignment_of(C++11)
rank(C++11)
extent(C++11)
Typ Modifikationen
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Type modifications
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remove_cv
remove_const
remove_volatile		(C++11)
(C++11)
(C++11)
add_cv
add_const
add_volatile		(C++11)
(C++11)
(C++11)
make_signed(C++11)
make_unsigned(C++11)
Typ Transformationen
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Type transformations
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aligned_storage(C++11)
aligned_union(C++11)
decay(C++11)
enable_if(C++11)
conditional(C++11)
common_type(C++11)
underlying_type(C++11)
result_of(C++11)
Typ-Trait-Konstanten
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Type trait constants
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integral_constant(C++11)
 
<tbody> </tbody>
definiert in Header <type_traits>
template< class T > struct is_abstract;
 (seit C++11)
Wenn T eine abstrakte Klasse (das heißt, eine Klasse, oder erklärt, erbt mindestens eine rein virtuelle Funktion) ist, stellt das Mitglied konstanten value gleich true. Für jede andere Art, value ist false .
Original:
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.
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Inherited from std::integral_constant

Member constants

value
[statisch]
true wenn T is an abstract class type , false anders
Original:
true if T is an abstract class type , false otherwise
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(public static Mitglied konstanten)

Member functions

operator bool
wandelt das Objekt bool, gibt value
Original:
converts the object to bool, returns value
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(öffentliche Elementfunktion)

Member types

Type
Original:
Type
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 Definition
value_type bool
type std::integral_constant<bool, value>

Notes

Abstrakte Klassen können nur als Basisklassen verwendet werden; keine Objekte einer abstrakten Klasse Typ kann außer in Form von Basisklasse Unterobjekte erstellt werden .
Original:
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.
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Eine abstrakte Klasse kann von einer Klasse, die nicht abstrakt ist, wenn eine rein virtuelle Funktion überschreibt eine virtuelle Funktion, die nicht rein abgeleitet werden .
Original:
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.
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Beispiel

#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

Siehe auch