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const_cast conversion

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Lenguaje C++
Los temas generales
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General topics
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Control de flujo
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Flow control
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Sentencias condicionales ejecución
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Conditional execution statements
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Instrucciones de iteración
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Iteration statements
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Ir declaraciones
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Jump statements
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Funciones
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Functions
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declaración de la función
lambda declaración de la función
función de plantilla
especificador inline
especificaciones de excepción (obsoleto)
noexcept especificador (C++11)
Excepciones
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Exceptions
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Los espacios de nombres
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Namespaces
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Tipos
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Types
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decltype specifier (C++11)
Los especificadores
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Specifiers
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cv especificadores
almacenamiento duración especificadores
constexpr especificador (C++11)
auto especificador (C++11)
alignas especificador (C++11)
Inicialización
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Initialization
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Los literales
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Literals
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Expresiones
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Expressions
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representaciones alternativas
Utilidades
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Utilities
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Tipos
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Types
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typedef declaration
alias de tipo de declaración (C++11)
atributos (C++11)
Lanza
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Casts
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conversiones implícitas
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
C-cast estilo y funcional
De asignación de memoria
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Memory allocation
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Clases
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Classes
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Clase propiedades específicas de la función
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Class-specific function properties
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Funciones especiales miembro
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Special member functions
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Plantillas
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Templates
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clase de plantilla
función de plantilla
plantilla de especialización
paquetes de parámetros (C++11)
Varios
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Miscellaneous
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Montaje en línea
 
Convierte entre los tipos con diferentes cv-cualificación .
Original:
Converts between types with different cv-qualification.
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Contenido

[editar] Sintaxis

const_cast < new_type > ( expression )
Devuelve un valor de tipo new_type .
Original:
Returns a value of type new_type.
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[editar] Explicación

Sólo las siguientes conversiones se puede hacer con const_cast. En particular, sólo const_cast se puede utilizar para desechar (eliminar) constness o volatilidad .
Original:
Only the following conversions can be done with const_cast. In particular, only const_cast may be used to cast away (remove) constness or volatility.
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1)
Dos punteros posiblemente varios niveles al mismo tipo se pueden convertir entre sí, independientemente de la CV-calificadores en cada nivel .
Original:
Two possibly multilevel pointers to the same type may be converted between each other, regardless of cv-qualifiers at each level.
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2)
lvalue de cualquier tipo T se puede convertir en una referencia lvalue o valor p para la T mismo tipo, más o menos cv-calificado. Del mismo modo, un valor p puede ser convertido a un valor p de referencia más o menos cv-cualificado .
Original:
lvalue of any type T may be converted to a lvalue or rvalue reference to the same type T, more or less cv-qualified. Likewise, an rvalue may be converted to a more or less cv-qualified rvalue reference.
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3)
Las mismas reglas se aplican a los punteros posiblemente varios niveles para los miembros de datos .
Original:
Same rules apply to possibly multilevel pointers to data members.
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4)
valor de puntero nulo se puede convertir en el valor de puntero nulo de new_type
Original:
null pointer value may be converted to the null pointer value of new_type
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Como con todas las expresiones de conversión, el resultado es:
Original:
As with all cast expressions, the result is:
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  • un valor-si new_type es un tipo de referencia o una referencia de valor-valor-poder funcionar en su tipo;
    Original:
    an lvalue if new_type is an lvalue reference type or an rvalue reference to function type;
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  • un xValue si new_type es una referencia a rvalue tipo de objeto;
    Original:
    an xvalue if new_type is an rvalue reference to object type;
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  • un prvalue de otra manera .
    Original:
    a prvalue otherwise.
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[editar] Notas

Punteros a funciones y punteros a funciones miembro no están sujetos a const_cast
Original:
Pointers to functions and pointers to member functions are not subject to const_cast
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A pesar de que const_cast podrá eliminar cualquier constness de puntero o de referencia, utilizando el puntero o referencia que resulta escribir en un objeto que se declaró const invoca un comportamiento indefinido .
Original:
Even though const_cast may remove constness from any pointer or reference, using the resulting pointer or reference to write to an object that was declared const invokes undefined behavior.
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[editar] Palabras clave

const_cast

[editar] Ejemplo

#include <iostream>
 
struct type {
    type() :i(3) {}
    void m1(int v) const {
        // this->i = v;                 // compile error: this is a pointer to const
        const_cast<type*>(this)->i = v; // OK
    }
    int i;
};
 
int main() 
{
    int i = 3;                    // i is not declared const
    const int& cref_i = i; 
    const_cast<int&>(cref_i) = 4; // OK: modifies i
    std::cout << "i = " << i << '\n';
 
    type t;
    t.m1(4);
    std::cout << "type::i = " << t.i << '\n';
 
    const int j = 3; // j is declared const
    int* pj = const_cast<int*>(&j);
    *pj = 4;         // undefined behavior!
 
    void (type::*mfp)(int) const = &type::m1; // pointer to member function
//  const_cast<void(type::*)(int)>(mfp); // compiler error: const_cast does not
                                         // work on function pointers
}

Output:

i = 4
type::i = 4

[editar] Ver también