default initialization
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Fournit la valeur initiale par dfaut pour un nouvel objet .
Original:
Provides the default initial value to a new object.
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Syntaxe
T object ;
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new T ;
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Explication
Initialisation par dfaut est effectue dans trois situations:
Original:
Default initialization is performed in three situations:
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1)
quand une variable avec la dure de stockage automatique est dclare sans initialisation
Original:
when a variable with automatic storage duration is declared with no initializer
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2)
quand un objet avec la dure de stockage dynamique est cre par une nouvelle expression sans un initialiseur
Original:
when an object with dynamic storage duration is created by a new-expression without an initializer
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3)
quand une classe de base ou un membre non statique de donnes n'est pas mentionn dans un liste d'initialisation constructeur et que le constructeur est appel .
Original:
when a base class or a non-static data member is not mentioned in a constructor liste d'initialisation and that constructor is called.
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Les effets de l'initialisation par dfaut sont les suivants:
Original:
The effects of default initialization are:
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- Si
Test un type de classe, le constructeur par dfaut est appel fournir la valeur initiale pour le nouvel objet .Original:IfTis a class type, the constructeur par dfaut is called to provide the initial value for the new object.The text has been machine-translated via Google Translate.
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- Si
Test un type tableau, chaque lment du tableau est initialis par dfaut .Original:IfTis an array type, every element of the array is default-initialized.The text has been machine-translated via Google Translate.
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- Sinon, rien n'est fait .Original:Otherwise, nothing is done.The text has been machine-translated via Google Translate.
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Si
T est un type const-qualifi, il doit tre d'un type classe avec un constructeur par dfaut fourni par l'utilisateur .Original:
If
T is a const-qualified type, it must be a class type with a user-provided default constructor.The text has been machine-translated via Google Translate.
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Notes
Initialisation par dfaut de non-classe des variables avec la dure de stockage automatique et dynamique produit des objets avec des valeurs indtermines (objets statiques et fil-locale se zro initialis)
Original:
Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-locale objects get zro initialis)
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Rfrence ne peut pas tre initialis par dfaut .
Original:
Reference cannot be default-initialized.
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Exemple
#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
}