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    default initialization

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    Initialization
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    Bietet die Standard-Ausgangswert zu einem neuen Objekt .
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    Provides the default initial value to a new object.
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    Inhaltsverzeichnis

    [Bearbeiten]Syntax

    Tobject; (1)
    new T; (2)

    [Bearbeiten]Erklärung

    Default-Initialisierung ist in drei Situationen durchgeführt:
    Original:
    Default initialization is performed in three situations:
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    1)
    wenn eine Variable mit automatischer Lagerdauer wird ohne Initialisierung deklariert
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    when a variable with automatic storage duration is declared with no initializer
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    2)
    wenn ein Objekt mit dynamischen Lagerdauer wird durch einen neuen Ausdruck ohne Initialisierung erstellt
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    when an object with dynamic storage duration is created by a new-expression without an initializer
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    3)
    wenn eine Basisklasse oder ein nicht-statisches Datenelement nicht in einem Konstruktor Initialisierungsliste erwähnt und dass Konstruktor aufgerufen wird .
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    when a base class or a non-static data member is not mentioned in a constructor Initialisierungsliste and that constructor is called.
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    Die Auswirkungen der Default-Initialisierung sind:
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    The effects of default initialization are:
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    • Wenn T eine Klasse-Typ ist, wird die Standardkonstruktor aufgerufen, um den ursprünglichen Wert für das neue Objekt bietet .
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      If T is a class type, the Standardkonstruktor is called to provide the initial value for the new object.
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    • Wenn T ein Array-Typ ist, ist jedes Element des Arrays standardmäßig initialisiert .
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      If T is an array type, every element of the array is default-initialized.
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    • Ansonsten wird nichts getan .
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      Otherwise, nothing is done.
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    Wenn T a const qualifizierten Typ ist, muss es eine Klasse-Typ mit einem vom Benutzer bereitgestellten Standardkonstruktor sein .
    Original:
    If T is a const-qualified type, it must be a class type with a user-provided default constructor.
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    [Bearbeiten]Notes

    Standard Initialisierung nicht Klassenvariablen mit automatischer und dynamischer Lagerdauer produziert Objekten mit unbestimmter (statische und Faden-locale Objekte erhalten Null initialisiert)
    Original:
    Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-locale objects get Null initialisiert)
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    Referenz nicht default-initialisiert werden .
    Original:
    Reference cannot be default-initialized.
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    [Bearbeiten]Beispiel

    #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 undeterminatestd::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 ctorconst T2 t2;// ok, calls the user-provided default ctor // t2.mem is default-initialized}


    [Bearbeiten]Siehe auch

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