default initialization

 

C++

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Lenguaje C++

Los temas generales Original: General topics The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
Preprocessor Comentarios Palabras clave	Tabla ASCII Las secuencias de escape Historia de C++
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if statement	switch statement
Instrucciones de iteración Original: Iteration statements The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
for loop range-for loop (C++11)	while loop do-while loop
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continue statement break statement	goto statement return statement
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espacio de nombres declaración	alias de espacios de nombres
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tipos fundamentales tipos de compuestos los tipos de enumeración	tipos de unión tipos de funciones
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cv especificadores
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constexpr especificador (C++11)
auto especificador (C++11)
alignas especificador (C++11)
Inicialización Original: Initialization The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
predeterminado de inicialización valor de inicialización cero de inicialización copiar inicialización inicialización directa	inicialización de agregados lista de inicialización (C++11) inicialización constante referencia de inicialización

Los literales Original: Literals The text has been machine-translated via Google Translate. You can help to correct and verify the translation. Click here for instructions.
literales enteros Los literales de caracteres Los literales de punto flotante literales de cadena	Los literales booleanos nullptr (C++11) definido por el usuario (C++11)
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clase de declaración this pointer acceder a los especificadores	amigo especificador listas de inicializadores
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Montaje en línea

 

Proporciona el valor inicial por defecto a un objeto nuevo .

Original:

Provides the default initial value to a new object.

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Sintaxis

T object ;	(1)
new T ;	(2)

Explicación

Inicialización por defecto se realiza en tres situaciones:

Original:

Default initialization is performed in three situations:

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1)

cuando una variable con el tiempo de almacenamiento automático se declara sin inicializador

Original:

when a variable with automatic storage duration is declared with no initializer

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2)

cuando un objeto con una duración de almacenamiento dinámico es creado por una nueva expresión sin un inicializador

Original:

when an object with dynamic storage duration is created by a new-expression without an initializer

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3)

cuando una clase base o un miembro no estático datos no se menciona en un inicializador lista constructor y que el constructor se llama .

Original:

when a base class or a non-static data member is not mentioned in a constructor inicializador lista and that constructor is called.

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Los efectos de la inicialización por defecto son:

Original:

The effects of default initialization are:

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• Si T es un tipo de clase, la default constructor está llamada a proporcionar el valor inicial para el nuevo objeto .

  Original:

  If T is a class type, the default constructor is called to provide the initial value for the new object.

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• Si T es un tipo de matriz, cada elemento de la matriz es inicializada por defecto .

  Original:

  If T is an array type, every element of the array is default-initialized.

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• De lo contrario, no se hace nada .

  Original:

  Otherwise, nothing is done.

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Si T es un tipo const cualificado, debe ser un tipo de clase con un constructor predeterminado proporcionado por el usuario .

Original:

If T is a const-qualified type, it must be a class type with a user-provided default constructor.

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Notas

Inicialización por defecto de la no-clase variables con el tiempo de almacenamiento automático y dinámico produce objetos con valores indeterminados (objetos estáticos e hilo locale-get cero inicializado)

Original:

Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-locale objects get cero inicializado)

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Referencia no puede ser inicializado por defecto .

Original:

Reference cannot be default-initialized.

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Ejemplo

#include <string>
struct T1 {};
class T2 { 
    int mem;
 public:
    T2() {} // "mem" not in initializer list
};
int n; // This is not default-initialization, the value is zero.
int main()
{
    int n;            // non-class: the value is undeterminate
    std::string s;    // calls default ctor, the value is "" (empty string)
    std::string a[2]; // calls default ctor, creates two empty strings
//    int& r;         // error: default-initializing a reference
//    const int n;    // error: const non-class type
//    const T1 nd;    // error: const class type with implicit ctor
    T1 t1; // ok, calls implicit default ctor
    const T2 t2; // ok, calls the user-provided default ctor 
                 // t2.mem is default-initialized
}

Ver también

• inicialización directa
• copiar inicialización
• lista de inicialización