default initialization
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Fournit la valeur initiale par défaut pour un nouvel objet .
Original:
Provides the default initial value to a new object.
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Sommaire |
[modifier] Syntaxe
T object ;
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(1) | ||||||||
new T ;
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[modifier] Explication
Initialisation par défaut est effectuée dans trois situations:
Original:
Default initialization is performed in three situations:
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1)
quand une variable avec la durée de stockage automatique est déclarée 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 durée de stockage dynamique est créée 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 données n'est pas mentionné dans un liste d'initialisation constructeur et que le constructeur est appelé .
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 défaut sont les suivants:
Original:
The effects of default initialization are:
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- Si
Test un type de classe, le constructeur par défaut est appelé à fournir la valeur initiale pour le nouvel objet .Original:IfTis a class type, the constructeur par défaut 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 élément du tableau est initialisé par défaut .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-qualifié, il doit être d'un type classe avec un constructeur par défaut 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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[modifier] Notes
Initialisation par défaut de non-classe des variables avec la durée de stockage automatique et dynamique produit des objets avec des valeurs indéterminées (objets statiques et fil-locale se zéro initialisé)
Original:
Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-locale objects get zéro initialisé)
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Référence ne peut pas être initialisé par défaut .
Original:
Reference cannot be default-initialized.
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[modifier] 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 }
