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default initialization

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C++
 
Linguaggio C + +
Temi generali
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General topics
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Controllo del flusso
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Flow control
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Dichiarazioni esecuzione condizionale
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Conditional execution statements
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Iterazione dichiarazioni
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Iteration statements
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Vai dichiarazioni
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Jump statements
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Funzioni
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Functions
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dichiarazione di funzione
lambda funzione dichiarazione
funzione di modello
specificatore inline
eccezioni specifiche (deprecato)
noexcept specificatore (C++11)
Eccezioni
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Exceptions
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Spazi dei nomi
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Namespaces
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Tipi
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Types
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decltype specifier (C++11)
Specifiers
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Specifiers
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cv specificatori
Durata di stoccaggio specificatori
constexpr specificatore (C++11)
specificatore auto (C++11)
alignas specificatore (C++11)
Inizializzazione
Original:
Initialization
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Letterali
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Literals
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Espressioni
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Expressions
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rappresentazioni alternative
Utilities
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Utilities
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Tipi
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Types
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typedef declaration
Tipo alias dichiarazione (C++11)
attributi (C++11)
Lancia
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Casts
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conversioni implicite
const_cast conversion
static_cast conversion
dynamic_cast conversion
reinterpret_cast conversion
Fusione C-stile e funzionale
Occupazione della memoria
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Memory allocation
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Classi
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Classes
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Specifiche per una classe di funzioni proprietà
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Class-specific function properties
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esplicito (C++11)
statico
Funzioni membro speciali
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Special member functions
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Modelli
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Templates
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classe template
funzione di modello
modello di specializzazione
parametri confezioni (C++11)
Varie
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Miscellaneous
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Montaggio in linea
 
Fornisce il valore iniziale di default per un nuovo oggetto.
Original:
Provides the default initial value to a new object.
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Indice

[modifica] Sintassi

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

[modifica] Spiegazione

Inizializzazione di default viene eseguita in tre situazioni:
Original:
Default initialization is performed in three situations:
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1)
quando una variabile con la durata di archiviazione automatica è dichiarata senza inizializzatore
Original:
when a variable with automatic storage duration is declared with no initializer
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2)
quando un oggetto con durata di stoccaggio dinamico viene creato un nuovo-espressione senza un inizializzatore
Original:
when an object with dynamic storage duration is created by a new-expression without an initializer
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3)
Quando una classe base o un membro non statico dati non è menzionato in un inizializzatore lista costruttore e che il costruttore si chiama.
Original:
when a base class or a non-static data member is not mentioned in a constructor inizializzatore lista and that constructor is called.
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Gli effetti di inizializzazione di default sono:
Original:
The effects of default initialization are:
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  • Se T è un tipo di classe, il costruttore di default è chiamato a fornire il valore iniziale per il nuovo oggetto.
    Original:
    If T is a class type, the costruttore di default is called to provide the initial value for the new object.
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  • Se T è un tipo di matrice, ogni elemento della matrice è default-inizializzato.
    Original:
    If T is an array type, every element of the array is default-initialized.
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  • In caso contrario, non si fa nulla.
    Original:
    Otherwise, nothing is done.
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Se T è un const tipo qualificato, deve essere un tipo di classe con un fornito dall'utente costruttore di default.
Original:
If T is a const-qualified type, it must be a class type with a user-provided default constructor.
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[modifica] Note

Inizializzazione di default di non di classe variabili con durata di memorizzazione automatica e dinamica produce oggetti con valori indeterminati (oggetti statici e filo-locale ottenere azzerare inizializzato)
Original:
Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-locale objects get azzerare inizializzato)
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Di riferimento non può essere inizializzato di default.
Original:
Reference cannot be default-initialized.
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[modifica] Esempio

#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
}


[modifica] Vedi anche

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