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std::is_empty

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< cpp‎ | types

 
 
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Operadores relacionales
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Pairs and tuples
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Swap, forward and move
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Tipos básicos
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Basic types
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Tipos fundamentales
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Límites numéricos
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Numeric limits
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Información de tipo en tiempo de ejecución
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Runtime type information
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Caracteres de tipo
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Type traits
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Categorías primarias de tipo
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Primary type categories
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Propiedades de tipo
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Type properties
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is_empty
(C++11)
Operaciones compatibles
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Supported operations
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Relaciones y consultas de propiedad
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Relationships and property queries
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Modificaciones de tipo
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Type modifications
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Transformaciones de tipo
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Type transformations
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Escriba constantes rasgos
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Type trait constants
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Definido en la cabecera <type_traits>
template< class T >
struct is_empty;
(desde C++11)
Si es en T tipo vacío (es decir, un tipo de clase no-unión con ninguno de los miembros no estáticos que no sean campos de bits de tamaño 0, no hay funciones virtuales, hay clases base virtuales y no las clases base no vacías), proporciona el miembro constante value true iguales. Para cualquier otro tipo, es value 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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Contenido

Inherited from std::integral_constant

Member constants

value
[estático]
true si T is an empty class type , false lo contrario
Original:
true if T is an empty class type , false otherwise
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(miembro público estático constante)

Member functions

operator bool
convierte el objeto a bool, devuelve value
Original:
converts the object to bool, returns value
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(función miembro público)

Member types

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

[editar] Notas

sizeof(T) siempre devuelve 1 si T está vacío, pero la herencia de clases base vacías general no aumenta el tamaño de una clase debido a la optimización de la base vacía .
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> y todos los otros rasgos de tipo son clases vacías .
Original:
std::is_empty<T> and all other type traits are empty classes.
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[editar] Ejemplo

#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';
}

Salida:

true
false
false

[editar] Ver también

(C++11)
checks if a type is a class type (but not union type)
(plantilla de clase) [editar]