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    std::is_empty

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    C++
     
    Utilities-Bibliothek
     
    Geben Sie Unterstützung
    Grundtypen
    Original:
    Basic types
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    Grundtypen
    Feste Breite Integer-Typen(C++11)
    Numerische Grenzen
    Original:
    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_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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    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)
    Typ-Trait-Konstanten
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    Type trait constants
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    integral_constant(C++11)
     
    definiert in Header <type_traits>
    template<class T >
    struct is_empty;
    		(seit C++11)
    Wenn T en leere Typ (das heißt, ein nicht gewerkschaftlich Klasse Typ ohne nicht-statische anderen Mitgliedern als Bit-Felder der Größe 0, keine virtuellen Funktionen, keine virtuellen Basisklassen, und keine nicht-leeren Basisklassen) ist, bietet das Mitglied konstanten value gleich true. Für jede andere Art, value ist false .
    Original:
    If T is en empty type (that is, a non-union class type with no non-static members other than bit-fields of size 0, no virtual functions, no virtual base classes, and no non-empty base classes), provides the member constant value equal true. For any other type, value is false.
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    Inhaltsverzeichnis

    Inherited from std::integral_constant

    Member constants

    value
    [statisch]
    true wenn T is an empty class type , false anders
    Original:
    true if T is an empty 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_typebool
    typestd::integral_constant<bool, value>

    [Bearbeiten]Notes

    sizeof(T) immer 1 zurück, wenn T leer ist, sondern erbt von leeren Basisklassen in der Regel nicht die Größe einer Klasse wegen leerer Sockel Optimierung .
    Original:
    sizeof(T) always returns 1 if T is empty, but inheriting from empty base classes usually does not increase the size of a class due to empty base optimization.
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    std::is_empty<T> und alle anderen Exterieur sind leer Klassen .
    Original:
    std::is_empty<T> and all other type traits are empty classes.
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    [Bearbeiten]Beispiel

    #include <iostream>#include <type_traits>   struct A {};   struct B {int m;};   struct C {virtual ~C();};   int main(){std::cout<<std::boolalpha;std::cout<< std::is_empty<A>::value<<'\n';std::cout<< std::is_empty<B>::value<<'\n';std::cout<< std::is_empty<C>::value<<'\n';}

    Output: 

    true false false

    [Bearbeiten]Siehe auch

    (C++11)
    		 checks if a type is a class type (but not union type)
    (Klassen-Template)[edit]
    Von „https://de.cppreference.com/mwiki/index.php?title=cpp/types/is_empty&oldid=30185“
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