std::is_empty – cppreference.com

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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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Inherited from std::integral_constant

Member constants


	`true` wenn `T` is an empty class type , `false` anders Original: `true` if `T` is an empty class type , `false` otherwise The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (public static Mitglied konstanten)

Member functions


	wandelt das Objekt `bool`, gibt `value` Original: converts the object to `bool`, returns `value` The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions. (öffentliche Elementfunktion)

Member types


Type Original: Type The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.	Definition

`value_type`	`bool`

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

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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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:

Siehe auch


	checks if a type is a class type (but not union type) (Klassen-Template) [edit]