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std::is_default_constructible, std::is_trivially_default_constructible, std::is_nothrow_default_constructible

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Tipos básicos
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Basic types
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Tipos fundamentales
Tipos fijos ancho enteros (C++11)
Límites numéricos
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Numeric limits
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C numérico limita interfaz
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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(C++11)
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Propiedades de tipo
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Type properties
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Operaciones compatibles
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Supported operations
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is_default_constructibleis_trivially_default_constructibleis_nothrow_default_constructible
(C++11)(C++11)(C++11)
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 el archivo de encabezado <type_traits>
template< class T >
struct is_default_constructible;
(1) (desde C++11)
template< class T >
struct is_trivially_default_constructible;
(2) (desde C++11)
template< class T >
struct is_nothrow_default_constructible;
(3) (desde C++11)
1)
Comprueba si un tipo es DefaultConstructible, es decir, tiene un constructor por defecto accesible explícito o implícito. Si el requisito se cumple, un miembro constante value true igual se proporciona, de lo contrario es value false .
Original:
Checks whether a type is DefaultConstructible, i.e. has an accessible explicit or implicit default constructor. If the requirement is met, a member constant value equal true is provided, otherwise value is false.
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2)
Igual que el 1), pero la expresión constructor no llama a ninguna operación que no es trivial .
Original:
Same as 1), but the constructor expression does not call any operation that is not trivial.
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3)
Igual que 1), pero la expresión constructor se noexcept .
Original:
Same as 1), but the constructor expression is noexcept.
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Contenido

Heredado de std::integral_constant

Constantes miembro

value
[estático]
true si T is default-constructible , de lo contrario, false
(miembro público estático constante)

Funciones miembro

operator bool
convierte el objeto a bool, devuelve value
(función miembro público)

Tipos miembro

Tipo Definición
value_type bool
type std::integral_constant<bool, value>

[editar] Posible implementación

template< class T>
struct is_default_constructible : std::is_constructible<T> {};
 
template< class T>
struct is_trivially_default_constructible : std::is_trivially_constructible<T> {};
 
template< class T>
struct is_nothrow_default_constructible : std::is_nothrow_constructible<T> {};

[editar] Ejemplo

#include <iostream>
#include <type_traits>
 
struct Ex1 {
    std::string str; // member has a non-trivial default ctor
};
struct Ex2 {
    int n;
    Ex2() = default; // trivial and non-throwing
};
 
int main() {
    std::cout << std::boolalpha << "Ex1 is default-constructible? "
              << std::is_default_constructible<Ex1>::value << '\n'
              << "Ex1 is trivially default-constructible? "
              << std::is_trivially_default_constructible<Ex1>::value << '\n'
              << "Ex2 is trivially default-constructible? "
              << std::is_trivially_default_constructible<Ex2>::value << '\n';
              << "Ex2 is nothrow default-constructible? "
              << std::is_nothrow_default_constructible<Ex2>::value << '\n';
}

Salida:

Ex1 is default-constructible? true
Ex1 is trivially default-constructible? false
Ex2 is trivially default-constructible? true
Ex2 is nothrow default-constructible? true

[editar] Ver también

Comprueba si un tipo tiene un constructor de argumentos concretos
Original:
checks if a type has a constructor for specific arguments
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(plantilla de clase) [editar]
Comprueba si un tipo tiene un constructor de copia
Original:
checks if a type has a copy constructor
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(plantilla de clase) [editar]
Comprueba si un tipo tiene un constructor movimiento
Original:
checks if a type has a move constructor
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(plantilla de clase) [editar]